revert exists(), unused

* re-organized command structure
* added 'dup' command

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,31 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: "[bug-report]"
+labels: bug
+assignees: TLINDEN
+
+---
+
+**Describtion**
+<!-- Please provide a clear and concise description of the issue: -->
+
+
+**Steps To Reproduce**
+<!-- Please detail the steps to reproduce the behavior: -->
+
+
+**Expected behavior**
+<!-- What do you expected to happen instead? -->
+
+
+**Version information**
+<!--
+Please provide as much version information as possible:
+- if you have just installed a binary, provide the output of: rpn -v
+- if you installed from source, provide the output of: make show-version
+- provide additional details: operating system and version and shell environment
+-->
+
+
+**Additional informations**

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,23 @@
+---
+name: Feature request
+about: Suggest a feature
+title: "[feature-request]"
+labels: feature-request
+assignees: TLINDEN
+
+---
+
+**Describtion**
+<!-- Please provide a clear and concise description of the feature you desire: -->
+
+
+
+**Version information**
+<!--
+Just in case the feature is already present, please provide as
+much version information as possible:
+- if you have just installed a binary, provide the output of: rpn -v
+- if you installed from source, provide the output of: make show-version
+- provide additional details: operating system and version and shell environment
+-->
+

.github/workflows/ci.yaml

@@ -0,0 +1,36 @@
+name: build-and-test-rpn
+on: [push, pull_request]
+jobs:
+  build:
+    strategy:
+      matrix:
+        version: [1.21]
+        os: [ubuntu-latest, windows-latest, macos-latest]
+    name: Build
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Set up Go
+      uses: actions/setup-go@v3
+      with:
+        go-version: ${{ matrix.version }}
+      id: go
+
+    - name: checkout
+      uses: actions/checkout@v3
+
+    - name: build
+      run: go build
+
+    - name: test
+      run: make test
+
+  golangci:
+    name: lint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/setup-go@v3
+        with:
+          go-version: 1.21
+      - uses: actions/checkout@v3
+      - name: golangci-lint
+        uses: golangci/golangci-lint-action@v3

.gitignore

@@ -1,3 +1,4 @@
 releases
 rpn
 rpn.1
+coverage.out

Makefile

@@ -39,10 +39,6 @@ ifdef HAVE_POD
 	  echo "var manpage = \`" >> $*.go
 	  pod2text $*.pod >> $*.go
 	  echo "\`" >> $*.go
-
-	  echo "var usage = \`" >> $*.go
-	  awk '/SYNOPS/{f=1;next} /DESCR/{f=0} f' $*.pod  | sed 's/^    //' >> $*.go
-	  echo "\`" >> $*.go
 endif
 
 buildlocal:
@@ -59,11 +55,10 @@ clean:
 
 test:
 	go test -v ./...
-	bash t/test.sh
 
 singletest:
-	@echo "Call like this: ''make singletest TEST=TestPrepareColumns MOD=lib"
+	@echo "Call like this: ''make singletest TEST=TestPrepareColumns"
-	go test -run $(TEST) github.com/tlinden/rpn/$(MOD)
+	go test -run $(TEST)
 
 cover-report:
 	go test ./... -cover -coverprofile=coverage.out
@@ -76,4 +71,16 @@ buildall:
 	./mkrel.sh $(tool) $(VERSION)
 
 release: buildall
-	gh release create $(VERSION) --generate-notes releases/*
+	gh release create v$(VERSION) --generate-notes releases/*
+
+show-versions: buildlocal
+	@echo "### rpn version:"
+	@./rpn -v
+
+	@echo
+	@echo "### go module versions:"
+	@go list -m all
+
+	@echo
+	@echo "### go version used for building:"
+	@grep -m 1 go go.mod

README.md

@@ -1,4 +1,8 @@
-## Reverse Polish Notation Calculator for the commandline
+## Programmable command-line calculator using reverse polish notation
+
+[![Actions](https://github.com/tlinden/rpnc/actions/workflows/ci.yaml/badge.svg)](https://github.com/tlinden/rpnc/actions)
+[![License](https://img.shields.io/badge/license-GPL-blue.svg)](https://github.com/tlinden/rpnc/blob/master/LICENSE)
+[![Go Report Card](https://goreportcard.com/badge/github.com/tlinden/rpnc)](https://goreportcard.com/report/github.com/tlinden/rpnc) 
 
 This is a small commandline calculator which takes its input in
 [reverse polish notation](https://en.wikipedia.org/wiki/Reverse_Polish_notation)
@@ -11,10 +15,18 @@ Features:
 - various stack manipulation commands
 - basic math operators
 - advanced math functions (not yet complete)
-- provides interactive repl
 - can be used on the commandline
 - can calculate data in batch mode (also from STDIN)
 - extensible with custom LUA functions
+- provides interactive repl
+- completion
+- history
+- comments (comment character is `#`)
+- variables
+
+## Demo
+
+![asciicast](demo/demo.gif)
 
 ## Working principle
 
@@ -65,6 +77,8 @@ DEBUG(012):      push to stack: 200.00
 = 200
 ```
 
+For a very good explanation how reverse polish notation and the stack works [watch this video by Prof. Brailsford](https://youtu.be/7ha78yWRDlE?si=9MCp59jAAG8fXavP)
+
 ## Usage
 
 Basically   you  enter   numbers  followed   by  an   operator  or   a
@@ -211,10 +225,15 @@ the `register()` function to register your functions to the
 calculator. This function takes these parameters:
 
 - function name
-- number of arguments expected (1,2 or -1 allowed), -1 means batch
+- number of arguments expected (see below)
-  mode
 - help text
 
+Number of expected arguments can be:
+
+- 0: expect 1 argument but do NOT modify the stack
+- 1-n: do a singular calculation
+- -1: batch mode work with all numbers on the stack 
+
 Please [refer to the lua language
 reference](https://www.lua.org/manual/5.4/) for more details about
 LUA.
@@ -254,9 +273,7 @@ hesitate to ask me about it, I'll add it.
 
 The  documentation  is  provided  as  a unix  man-page.   It  will  be
 automatically installed if  you install from source.  However, you can
-read the man-page online:
+[read the man-page online](https://github.com/TLINDEN/rpnc/blob/master/rpn.pod)
-
-https://github.com/TLINDEN/rpnc/blob/main/rpn.pod
 
 Or if you cloned  the repository you can read it  this way (perl needs
 to be installed though): `perldoc rpn.pod`.

calc.go

@@ -20,9 +20,8 @@ package main
 import (
 	"errors"
 	"fmt"
-	"math"
-	"os"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -30,57 +29,66 @@ import (
 )
 
 type Calc struct {
-	debug          bool
+	debug        bool
-	batch          bool
+	batch        bool
-	stdin          bool
+	stdin        bool
-	stack          *Stack
+	showstack    bool
-	history        []string
+	intermediate bool
-	completer      readline.AutoCompleter
+	notdone      bool // set to true as long as there are items left in the eval loop
-	interpreter    *Interpreter
+	stack        *Stack
-	Operators      *regexp.Regexp
+	history      []string
-	Space          *regexp.Regexp
+	completer    readline.AutoCompleter
-	Constants      []string
+	interpreter  *Interpreter
-	MathFunctions  []string
+	Space        *regexp.Regexp
-	BatchFunctions []string
+	Comment      *regexp.Regexp
-	LuaFunctions   []string
+	Register     *regexp.Regexp
+	Constants    []string
+	LuaFunctions []string
+
+	Funcalls      Funcalls
+	BatchFuncalls Funcalls
+
+	// different kinds of commands, displays nicer in help output
+	StackCommands    Commands
+	SettingsCommands Commands
+	ShowCommands     Commands
+	Commands         Commands
+
+	Vars map[string]float64
 }
 
 // help for lua functions will be added dynamically
-const Help string = `Available commands:
+const Help string = `
-batch                toggle batch mode
+Operators:
-debug                toggle debug output
+basic operators: + - x * / ^  (* is an alias of x)
-dump                 display the stack contents
-clear                clear the whole stack
-shift                remove the last element of the stack
-history              display calculation history
-help|?               show this message
-quit|exit|c-d|c-c    exit program
 
-Available operators:
+Percent functions:
-basic operators: + - x /
-
-Available math functions:
-sqrt                 square root
-mod                  remainder of division (alias: remainder)
-max                  batch mode only: max of all values
-min                  batch mode only: min of all values
-mean                 batch mode only: mean of all values (alias: avg)
-median               batch mode only: median of all values
 %                    percent
 %-                   substract percent
 %+                   add percent
 
-Math operators:
+Math functions (see https://pkg.go.dev/math):
-^                    power`
+mod sqrt abs acos acosh asin asinh atan atan2 atanh cbrt ceil cos cosh
+erf erfc  erfcinv erfinv exp  exp2 expm1 floor  gamma ilogb j0  j1 log
+log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
+y1 copysign dim hypot
+
+Batch functions:
+sum                  sum of all values (alias: +)
+max                  max of all values
+min                  min of all values
+mean                 mean of all values (alias: avg)
+median               median of all values
+
+Register variables:
+>NAME                Put last stack element into variable NAME
+<NAME                Retrieve variable NAME and put onto stack`
 
 // commands, constants and operators,  defined here to feed completion
 // and our mode switch in Eval() dynamically
 const (
-	Commands       string = `dump reverse debug undebug clear batch shift undo help history manual exit quit`
+	//Commands  string = `dump reverse clear shift undo help history manual exit quit swap debug undebug nodebug batch nobatch showstack noshowstack vars`
-	Operators      string = `+ - * x / ^ % %- %+`
+	Constants string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
-	MathFunctions  string = `sqrt remainder`
-	Constants      string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
-	BatchFunctions string = `median avg mean max min`
 )
 
 // That way we can add custom functions to completion
@@ -92,53 +100,77 @@ func GetCompleteCustomFunctions() func(string) []string {
 			completions = append(completions, luafunc)
 		}
 
-		completions = append(completions, strings.Split(Commands, " ")...)
-		completions = append(completions, strings.Split(Operators, " ")...)
-		completions = append(completions, strings.Split(MathFunctions, " ")...)
 		completions = append(completions, strings.Split(Constants, " ")...)
 
 		return completions
 	}
 }
 
+func (c *Calc) GetCompleteCustomFuncalls() func(string) []string {
+	return func(line string) []string {
+		completions := []string{}
+
+		for function := range c.Funcalls {
+			completions = append(completions, function)
+		}
+
+		for function := range c.BatchFuncalls {
+			completions = append(completions, function)
+		}
+
+		for command := range c.SettingsCommands {
+			completions = append(completions, command)
+		}
+
+		for command := range c.ShowCommands {
+			completions = append(completions, command)
+		}
+
+		for command := range c.StackCommands {
+			completions = append(completions, command)
+		}
+
+		for command := range c.Commands {
+			completions = append(completions, command)
+		}
+
+		return completions
+	}
+
+}
+
 func NewCalc() *Calc {
 	c := Calc{stack: NewStack(), debug: false}
 
+	c.Funcalls = DefineFunctions()
+	c.BatchFuncalls = DefineBatchFunctions()
+	c.Vars = map[string]float64{}
+
 	c.completer = readline.NewPrefixCompleter(
 		// custom lua functions
 		readline.PcItemDynamic(GetCompleteCustomFunctions()),
+		readline.PcItemDynamic(c.GetCompleteCustomFuncalls()),
 	)
 
-	// pre-calculate mode switching regexes
-	reg := `^[`
-	for _, op := range strings.Split(Operators, " ") {
-		switch op {
-		case "x":
-			reg += op
-		default:
-			reg += `\` + op
-		}
-	}
-	reg += `]$`
-	c.Operators = regexp.MustCompile(reg)
-
 	c.Space = regexp.MustCompile(`\s+`)
+	c.Comment = regexp.MustCompile(`#.*`) // ignore everything after #
+	c.Register = regexp.MustCompile(`^([<>])([A-Z][A-Z0-9]*)`)
 
 	// pre-calculate mode switching arrays
 	c.Constants = strings.Split(Constants, " ")
-	c.MathFunctions = strings.Split(MathFunctions, " ")
-	c.BatchFunctions = strings.Split(BatchFunctions, " ")
 
-	for name := range LuaFuncs {
+	c.SetCommands()
-		c.LuaFunctions = append(c.LuaFunctions, name)
-	}
 
 	return &c
 }
 
-// setup the interpreter, called from main()
+// setup the interpreter, called from main(), import lua functions
 func (c *Calc) SetInt(I *Interpreter) {
 	c.interpreter = I
+
+	for name := range LuaFuncs {
+		c.LuaFunctions = append(c.LuaFunctions, name)
+	}
 }
 
 func (c *Calc) ToggleDebug() {
@@ -156,14 +188,21 @@ func (c *Calc) ToggleStdin() {
 	c.stdin = !c.stdin
 }
 
+func (c *Calc) ToggleShow() {
+	c.showstack = !c.showstack
+}
+
 func (c *Calc) Prompt() string {
 	p := "\033[31m»\033[0m "
 	b := ""
+
 	if c.batch {
 		b = "->batch"
 	}
+
 	d := ""
 	v := ""
+
 	if c.debug {
 		d = "->debug"
 		v = fmt.Sprintf("/rev%d", c.stack.rev)
@@ -174,25 +213,28 @@ func (c *Calc) Prompt() string {
 
 // the actual work horse, evaluate a line of calc command[s]
 func (c *Calc) Eval(line string) {
-	line = strings.TrimSpace(line)
+	// remove surrounding whitespace and comments, if any
+	line = strings.TrimSpace(c.Comment.ReplaceAllString(line, ""))
 
 	if line == "" {
 		return
 	}
 
-	for _, item := range c.Space.Split(line, -1) {
+	items := c.Space.Split(line, -1)
+
+	for pos, item := range items {
+		if pos+1 < len(items) {
+			c.notdone = true
+		} else {
+			c.notdone = false
+		}
+
 		num, err := strconv.ParseFloat(item, 64)
 
 		if err == nil {
 			c.stack.Backup()
 			c.stack.Push(num)
 		} else {
-			if c.Operators.MatchString(item) {
-				// simple ops like + or x
-				c.simple(item[0])
-				continue
-			}
-
 			if contains(c.Constants, item) {
 				// put the constant onto the stack
 				c.stack.Backup()
@@ -200,68 +242,157 @@ func (c *Calc) Eval(line string) {
 				continue
 			}
 
-			if contains(c.MathFunctions, item) {
+			if _, ok := c.Funcalls[item]; ok {
-				// go builtin math function, if implemented
+				if err := c.DoFuncall(item); err != nil {
-				c.mathfunc(item)
+					fmt.Println(err)
+				} else {
+					c.Result()
+				}
 				continue
 			}
 
-			if contains(c.BatchFunctions, item) {
+			if c.batch {
-				// math functions only supported in batch mode like max or mean
+				if _, ok := c.BatchFuncalls[item]; ok {
-				c.batchfunc(item)
+					if err := c.DoFuncall(item); err != nil {
-				continue
+						fmt.Println(err)
+					} else {
+						c.Result()
+					}
+					continue
+				}
+			} else {
+				if _, ok := c.BatchFuncalls[item]; ok {
+					fmt.Println("only supported in batch mode")
+					continue
+				}
 			}
 
 			if contains(c.LuaFunctions, item) {
 				// user provided custom lua functions
-				c.luafunc(item)
+				c.EvalLuaFunction(item)
+				continue
+			}
+
+			regmatches := c.Register.FindStringSubmatch(item)
+			if len(regmatches) == 3 {
+				switch regmatches[1] {
+				case ">":
+					c.PutVar(regmatches[2])
+				case "<":
+					c.GetVar(regmatches[2])
+				}
+				continue
+			}
+
+			// internal commands
+			if _, ok := c.Commands[item]; ok {
+				c.Commands[item].Func(c)
+				continue
+			}
+
+			if _, ok := c.ShowCommands[item]; ok {
+				c.ShowCommands[item].Func(c)
+				continue
+			}
+
+			if _, ok := c.StackCommands[item]; ok {
+				c.StackCommands[item].Func(c)
+				continue
+			}
+
+			if _, ok := c.SettingsCommands[item]; ok {
+				c.SettingsCommands[item].Func(c)
 				continue
 			}
 
-			// management commands
 			switch item {
 			case "?":
 				fallthrough
 			case "help":
-				fmt.Println(Help)
+				c.PrintHelp()
-				fmt.Println("Lua functions:")
+
-				for name, function := range LuaFuncs {
-					fmt.Printf("%-20s %s\n", name, function.help)
-				}
-			case "dump":
-				c.stack.Dump()
-			case "debug":
-				c.ToggleDebug()
-			case "undebug":
-				c.debug = false
-			case "batch":
-				c.ToggleBatch()
-			case "clear":
-				c.stack.Backup()
-				c.stack.Clear()
-			case "shift":
-				c.stack.Backup()
-				c.stack.Shift()
-			case "reverse":
-				c.stack.Backup()
-				c.stack.Reverse()
-			case "undo":
-				c.stack.Restore()
-			case "history":
-				for _, entry := range c.history {
-					fmt.Println(entry)
-				}
-			case "exit":
-				fallthrough
-			case "quit":
-				os.Exit(0)
-			case "manual":
-				man()
 			default:
 				fmt.Println("unknown command or operator!")
 			}
 		}
 	}
+
+	if c.showstack && !c.stdin {
+		dots := ""
+
+		if c.stack.Len() > 5 {
+			dots = "... "
+		}
+		last := c.stack.Last(5)
+		fmt.Printf("stack: %s%s\n", dots, list2str(last))
+	}
+}
+
+// Execute a math function, check if it is defined just in case
+func (c *Calc) DoFuncall(funcname string) error {
+	var function *Funcall
+	if c.batch {
+		function = c.BatchFuncalls[funcname]
+	} else {
+		function = c.Funcalls[funcname]
+	}
+
+	if function == nil {
+		panic("function not defined but in completion list")
+	}
+
+	var args Numbers
+	batch := false
+
+	if function.Expectargs == -1 {
+		// batch mode, but always < stack len, so check first
+		args = c.stack.All()
+		batch = true
+	} else {
+		//  this is way better behavior than just using 0 in place of
+		// non-existing stack items
+		if c.stack.Len() < function.Expectargs {
+			return errors.New("stack doesn't provide enough arguments")
+		}
+
+		args = c.stack.Last(function.Expectargs)
+	}
+
+	c.Debug(fmt.Sprintf("calling %s with args: %v", funcname, args))
+
+	// the  actual lambda call, so  to say. We provide  a slice of
+	// the requested size, fetched  from the stack (but not popped
+	// yet!)
+	R := function.Func(args)
+
+	if R.Err != nil {
+		// leave the stack untouched in case of any error
+		return R.Err
+	}
+
+	// don't forget to backup!
+	c.stack.Backup()
+
+	// "pop"
+	if batch {
+		// get rid of stack
+		c.stack.Clear()
+	} else {
+		// remove operands
+		c.stack.Shift(function.Expectargs)
+	}
+
+	// save result
+	c.stack.Push(R.Res)
+
+	// thanks a lot
+	c.SetHistory(funcname, args, R.Res)
+	return nil
+}
+
+// we need to add a history entry for each operation
+func (c *Calc) SetHistory(op string, args Numbers, res float64) {
+	c.History("%s %s -> %f", list2str(args), op, res)
 }
 
 // just a textual representation of math operations, viewable with the
@@ -272,13 +403,18 @@ func (c *Calc) History(format string, args ...any) {
 
 // print the result
 func (c *Calc) Result() float64 {
-	if !c.stdin {
+	// we only  print the result if it's either  a final result or
-		fmt.Print("= ")
+	// (if it is intermediate) if -i has been given
+	if c.intermediate || !c.notdone {
+		// only needed in repl
+		if !c.stdin {
+			fmt.Print("= ")
+		}
+
+		fmt.Println(c.stack.Last()[0])
 	}
 
-	fmt.Println(c.stack.Last())
+	return c.stack.Last()[0]
-
-	return c.stack.Last()
 }
 
 func (c *Calc) Debug(msg string) {
@@ -287,176 +423,18 @@ func (c *Calc) Debug(msg string) {
 	}
 }
 
-// do simple calculations
+func (c *Calc) EvalLuaFunction(funcname string) {
-func (c *Calc) simple(op byte) {
-	c.stack.Backup()
-
-	for c.stack.Len() > 1 {
-		b := c.stack.Pop()
-		a := c.stack.Pop()
-		var x float64
-
-		c.Debug(fmt.Sprintf("evaluating: %.2f %c %.2f", a, op, b))
-
-		switch op {
-		case '+':
-			x = a + b
-		case '-':
-			x = a - b
-		case 'x':
-			fallthrough // alias for *
-		case '*':
-			x = a * b
-		case '/':
-			if b == 0 {
-				fmt.Println("error: division by null!")
-				return
-			}
-			x = a / b
-		case '^':
-			x = math.Pow(a, b)
-		default:
-			panic("invalid operator!")
-		}
-
-		c.stack.Push(x)
-
-		c.History("%f %c %f = %f", a, op, b, x)
-
-		if !c.batch {
-			break
-		}
-	}
-
-	c.Result()
-}
-
-// calc using go math lib functions
-func (c *Calc) mathfunc(funcname string) {
-	c.stack.Backup()
-
-	for c.stack.Len() > 0 {
-		var x float64
-
-		switch funcname {
-		case "sqrt":
-			a := c.stack.Pop()
-			x = math.Sqrt(a)
-			c.History("sqrt(%f) = %f", a, x)
-
-		case "mod":
-			fallthrough // alias
-		case "remainder":
-			b := c.stack.Pop()
-			a := c.stack.Pop()
-			x = math.Remainder(a, b)
-			c.History("remainderf(%f / %f) = %f", a, b, x)
-
-		case "%":
-			b := c.stack.Pop()
-			a := c.stack.Pop()
-
-			x = (a / 100) * b
-			c.History("%f percent of %f = %f", b, a, x)
-
-		case "%-":
-			b := c.stack.Pop()
-			a := c.stack.Pop()
-
-			x = a - ((a / 100) * b)
-			c.History("%f minus %f percent of %f = %f", a, b, a, x)
-
-		case "%+":
-			b := c.stack.Pop()
-			a := c.stack.Pop()
-
-			x = a + ((a / 100) * b)
-			c.History("%f plus %f percent of %f = %f", a, b, a, x)
-
-		}
-
-		c.stack.Push(x)
-
-		if !c.batch {
-			break
-		}
-	}
-
-	c.Result()
-}
-
-// execute pure batch functions, operating on the whole stack
-func (c *Calc) batchfunc(funcname string) {
-	if !c.batch {
-		fmt.Println("error: only available in batch mode")
-	}
-
-	c.stack.Backup()
-	var x float64
-	count := c.stack.Len()
-
-	switch funcname {
-	case "median":
-		all := []float64{}
-
-		for c.stack.Len() > 0 {
-			all = append(all, c.stack.Pop())
-		}
-
-		middle := count / 2
-
-		x = all[middle]
-		c.History("median(all)")
-
-	case "mean":
-		fallthrough // alias
-	case "avg":
-		var sum float64
-
-		for c.stack.Len() > 0 {
-			sum += c.stack.Pop()
-		}
-
-		x = sum / float64(count)
-		c.History("avg(all)")
-	case "min":
-		x = c.stack.Pop() // initialize with the last one
-
-		for c.stack.Len() > 0 {
-			val := c.stack.Pop()
-			if val < x {
-				x = val
-			}
-		}
-
-		c.History("min(all)")
-	case "max":
-		x = c.stack.Pop() // initialize with the last one
-
-		for c.stack.Len() > 0 {
-			val := c.stack.Pop()
-			if val > x {
-				x = val
-			}
-		}
-
-		c.History("max(all)")
-	}
-
-	c.stack.Push(x)
-	_ = c.Result()
-}
-
-func (c *Calc) luafunc(funcname string) {
 	// called from calc loop
 	var x float64
 	var err error
 
 	switch c.interpreter.FuncNumArgs(funcname) {
+	case 0:
+		fallthrough
 	case 1:
-		x, err = c.interpreter.CallLuaFunc(funcname, []float64{c.stack.Last()})
+		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last())
 	case 2:
-		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.LastTwo())
+		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last(2))
 	case -1:
 		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.All())
 	default:
@@ -470,7 +448,15 @@ func (c *Calc) luafunc(funcname string) {
 
 	c.stack.Backup()
 
+	dopush := true
+
 	switch c.interpreter.FuncNumArgs(funcname) {
+	case 0:
+		a := c.stack.Last()
+		if len(a) == 1 {
+			c.History("%s(%f) = %f", funcname, a, x)
+		}
+		dopush = false
 	case 1:
 		a := c.stack.Pop()
 		c.History("%s(%f) = %f", funcname, a, x)
@@ -483,7 +469,78 @@ func (c *Calc) luafunc(funcname string) {
 		c.History("%s(*) = %f", funcname, x)
 	}
 
-	c.stack.Push(x)
+	if dopush {
+		c.stack.Push(x)
+	}
 
 	c.Result()
 }
+
+func (c *Calc) PutVar(name string) {
+	last := c.stack.Last()
+
+	if len(last) == 1 {
+		c.Debug(fmt.Sprintf("register %.2f in %s", last[0], name))
+		c.Vars[name] = last[0]
+	} else {
+		fmt.Println("empty stack")
+	}
+}
+
+func (c *Calc) GetVar(name string) {
+	if _, ok := c.Vars[name]; ok {
+		c.Debug(fmt.Sprintf("retrieve %.2f from %s", c.Vars[name], name))
+		c.stack.Backup()
+		c.stack.Push(c.Vars[name])
+	} else {
+		fmt.Println("variable doesn't exist")
+	}
+}
+
+func sortcommands(hash Commands) []string {
+	keys := make([]string, 0, len(hash))
+
+	for key := range hash {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	return keys
+}
+
+func (c *Calc) PrintHelp() {
+	fmt.Println("Available configuration commands:")
+	for _, name := range sortcommands(c.SettingsCommands) {
+		fmt.Printf("%-20s %s\n", name, c.SettingsCommands[name].Help)
+	}
+	fmt.Println()
+
+	fmt.Println("Available show commands:")
+	for _, name := range sortcommands(c.ShowCommands) {
+		fmt.Printf("%-20s %s\n", name, c.ShowCommands[name].Help)
+	}
+	fmt.Println()
+
+	fmt.Println("Available stack manipulation commands:")
+	for _, name := range sortcommands(c.StackCommands) {
+		fmt.Printf("%-20s %s\n", name, c.StackCommands[name].Help)
+	}
+	fmt.Println()
+
+	fmt.Println("Other commands:")
+	for _, name := range sortcommands(c.Commands) {
+		fmt.Printf("%-20s %s\n", name, c.Commands[name].Help)
+	}
+	fmt.Println()
+
+	fmt.Println(Help)
+
+	// append lua functions, if any
+	if len(LuaFuncs) > 0 {
+		fmt.Println("Lua functions:")
+		for name, function := range LuaFuncs {
+			fmt.Printf("%-20s %s\n", name, function.help)
+		}
+	}
+}

calc_test.go

@@ -0,0 +1,313 @@
+/*
+Copyright © 2023 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package main
+
+import (
+	"fmt"
+	"testing"
+
+	lua "github.com/yuin/gopher-lua"
+)
+
+func TestCommentsAndWhitespace(t *testing.T) {
+	calc := NewCalc()
+
+	var tests = []struct {
+		name string
+		cmd  []string
+		exp  float64 // last element of the stack
+	}{
+		{
+			name: "whitespace prefix",
+			cmd:  []string{"  5"},
+			exp:  5.0,
+		},
+		{
+			name: "whitespace postfix",
+			cmd:  []string{"5  "},
+			exp:  5.0,
+		},
+		{
+			name: "whitespace both",
+			cmd:  []string{"  5   "},
+			exp:  5.0,
+		},
+		{
+			name: "comment line w/ spaces",
+			cmd:  []string{"5", "   #   19"},
+			exp:  5.0,
+		},
+		{
+			name: "comment line w/o spaces",
+			cmd:  []string{"5", `#19`},
+			exp:  5.0,
+		},
+		{
+			name: "inline comment w/ spaces",
+			cmd:  []string{"5   #   19"},
+			exp:  5.0,
+		},
+		{
+			name: "inline comment w/o spaces",
+			cmd:  []string{"5#19"},
+			exp:  5.0,
+		},
+	}
+
+	for _, tt := range tests {
+		testname := fmt.Sprintf("%s .(expect %.2f)",
+			tt.name, tt.exp)
+
+		t.Run(testname, func(t *testing.T) {
+			for _, line := range tt.cmd {
+				calc.Eval(line)
+			}
+			got := calc.stack.Last()
+
+			if len(got) > 0 {
+				if got[0] != tt.exp {
+					t.Errorf("parsing failed:\n+++  got: %f\n--- want: %f",
+						got, tt.exp)
+				}
+			}
+
+			if calc.stack.Len() != 1 {
+				t.Errorf("invalid stack size:\n+++  got: %d\n--- want: 1",
+					calc.stack.Len())
+			}
+
+		})
+
+		calc.stack.Clear()
+	}
+}
+
+func TestCalc(t *testing.T) {
+	calc := NewCalc()
+
+	var tests = []struct {
+		name  string
+		cmd   string
+		exp   float64
+		batch bool
+	}{
+		// ops
+		{
+			name: "plus",
+			cmd:  `15 15 +`,
+			exp:  30,
+		},
+		{
+			name: "power",
+			cmd:  `4 2 ^`,
+			exp:  16,
+		},
+		{
+			name: "minus",
+			cmd:  `100 50 -`,
+			exp:  50,
+		},
+		{
+			name: "multi",
+			cmd:  `4 4 x`,
+			exp:  16,
+		},
+		{
+			name: "divide",
+			cmd:  `10 2 /`,
+			exp:  5,
+		},
+		{
+			name: "percent",
+			cmd:  `400 20 %`,
+			exp:  80,
+		},
+		{
+			name: "percent-minus",
+			cmd:  `400 20 %-`,
+			exp:  320,
+		},
+		{
+			name: "percent-plus",
+			cmd:  `400 20 %+`,
+			exp:  480,
+		},
+
+		// math tests
+		{
+			name: "mod",
+			cmd:  `9 2 mod`,
+			exp:  1,
+		},
+		{
+			name: "sqrt",
+			cmd:  `16 sqrt`,
+			exp:  4,
+		},
+		{
+			name: "ceil",
+			cmd:  `15.5 ceil`,
+			exp:  16,
+		},
+		{
+			name: "dim",
+			cmd:  `6 4 dim`,
+			exp:  2,
+		},
+
+		// constants tests
+		{
+			name: "pitimes2",
+			cmd:  `Pi 2 *`,
+			exp:  6.283185307179586,
+		},
+		{
+			name: "pi+sqrt2",
+			cmd:  `Pi Sqrt2 +`,
+			exp:  4.555806215962888,
+		},
+
+		// batch tests
+		{
+			name:  "batch-sum",
+			cmd:   `2 2 2 2 sum`,
+			exp:   8,
+			batch: true,
+		},
+		{
+			name:  "batch-median",
+			cmd:   `1 2 3 4 5 median`,
+			exp:   3,
+			batch: true,
+		},
+		{
+			name:  "batch-mean",
+			cmd:   `2 2 8 2 2 mean`,
+			exp:   3.2,
+			batch: true,
+		},
+		{
+			name:  "batch-min",
+			cmd:   `1 2 3 4 5 min`,
+			exp:   1,
+			batch: true,
+		},
+		{
+			name:  "batch-max",
+			cmd:   `1 2 3 4 5 max`,
+			exp:   5,
+			batch: true,
+		},
+
+		// stack tests
+		{
+			name: "use-vars",
+			cmd:  `10 >TEN clear 5 <TEN *`,
+			exp:  50,
+		},
+		{
+			name: "reverse",
+			cmd:  `100 500 reverse -`,
+			exp:  400,
+		},
+		{
+			name: "swap",
+			cmd:  `2 16 swap /`,
+			exp:  8,
+		},
+		{
+			name:  "clear batch",
+			cmd:   "1 1 1 1 1 clear 1 1 sum",
+			exp:   2,
+			batch: true,
+		},
+		{
+			name: "undo",
+			cmd:  `4 4 + undo *`,
+			exp:  16,
+		},
+	}
+
+	for _, tt := range tests {
+		testname := fmt.Sprintf("cmd-%s-expect-%.2f",
+			tt.name, tt.exp)
+
+		t.Run(testname, func(t *testing.T) {
+			calc.batch = tt.batch
+			calc.Eval(tt.cmd)
+			got := calc.Result()
+			calc.stack.Clear()
+			if got != tt.exp {
+				t.Errorf("calc failed:\n+++  got: %f\n--- want: %f",
+					got, tt.exp)
+			}
+		})
+	}
+}
+
+func TestCalcLua(t *testing.T) {
+	var tests = []struct {
+		function string
+		stack    []float64
+		exp      float64
+	}{
+		{
+			function: "lower",
+			stack:    []float64{5, 6},
+			exp:      5.0,
+		},
+		{
+			function: "parallelresistance",
+			stack:    []float64{100, 200, 300},
+			exp:      54.54545454545455,
+		},
+	}
+
+	calc := NewCalc()
+	L = lua.NewState(lua.Options{SkipOpenLibs: true})
+	defer L.Close()
+
+	luarunner := NewInterpreter("example.lua", false)
+	luarunner.InitLua()
+	calc.SetInt(luarunner)
+
+	for _, tt := range tests {
+		testname := fmt.Sprintf("lua-%s", tt.function)
+
+		t.Run(testname, func(t *testing.T) {
+			calc.stack.Clear()
+			for _, item := range tt.stack {
+				calc.stack.Push(item)
+			}
+
+			calc.EvalLuaFunction(tt.function)
+
+			got := calc.stack.Last()
+
+			if calc.stack.Len() != 1 {
+				t.Errorf("invalid stack size:\n+++  got: %d\n--- want: 1",
+					calc.stack.Len())
+			}
+
+			if got[0] != tt.exp {
+				t.Errorf("lua function %s failed:\n+++  got: %f\n--- want: %f",
+					tt.function, got, tt.exp)
+			}
+		})
+	}
+}

command.go

@@ -0,0 +1,201 @@
+/*
+Copyright © 2023 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+type CommandFunction func(*Calc)
+
+type Command struct {
+	Help string
+	Func CommandFunction
+}
+
+type Commands map[string]*Command
+
+func NewCommand(help string, function CommandFunction) *Command {
+	return &Command{
+		Help: help,
+		Func: function,
+	}
+}
+
+// define all management (that is: non calculation) commands
+func (c *Calc) SetCommands() {
+	c.SettingsCommands = Commands{
+		// Toggles
+		"debug": NewCommand(
+			"toggle debugging",
+			func(c *Calc) {
+				c.ToggleDebug()
+			},
+		),
+
+		"nodebug": NewCommand(
+			"disable debugging",
+			func(c *Calc) {
+				c.debug = false
+				c.stack.debug = false
+			},
+		),
+
+		"batch": NewCommand(
+			"toggle batch mode",
+			func(c *Calc) {
+				c.ToggleBatch()
+			},
+		),
+
+		"nobatch": NewCommand(
+			"disable batch mode",
+			func(c *Calc) {
+				c.batch = false
+			},
+		),
+
+		"showstack": NewCommand(
+			"toggle show last 5 items of the stack",
+			func(c *Calc) {
+				c.ToggleShow()
+			},
+		),
+
+		"noshowstack": NewCommand(
+			"disable display of the stack",
+			func(c *Calc) {
+				c.showstack = false
+			},
+		),
+	}
+
+	c.ShowCommands = Commands{
+		// Display commands
+		"dump": NewCommand(
+			"display the stack contents",
+			func(c *Calc) {
+				c.stack.Dump()
+			},
+		),
+
+		"history": NewCommand(
+			"display calculation history",
+			func(c *Calc) {
+				for _, entry := range c.history {
+					fmt.Println(entry)
+				}
+			},
+		),
+
+		"vars": NewCommand(
+			"show list of variables",
+			func(c *Calc) {
+				if len(c.Vars) > 0 {
+					fmt.Printf("%-20s     %s\n", "VARIABLE", "VALUE")
+					for k, v := range c.Vars {
+						fmt.Printf("%-20s  -> %.2f\n", k, v)
+					}
+				} else {
+					fmt.Println("no vars registered")
+				}
+			},
+		),
+	}
+
+	c.StackCommands = Commands{
+		"clear": NewCommand(
+			"clear the whole stack",
+			func(c *Calc) {
+				c.stack.Backup()
+				c.stack.Clear()
+			},
+		),
+
+		"shift": NewCommand(
+			"remove the last element of the stack",
+			func(c *Calc) {
+				c.stack.Backup()
+				c.stack.Shift()
+			},
+		),
+
+		"reverse": NewCommand(
+			"reverse the stack elements",
+			func(c *Calc) {
+				c.stack.Backup()
+				c.stack.Reverse()
+			},
+		),
+
+		"swap": NewCommand(
+			"exchange the last two elements",
+			func(c *Calc) {
+				if c.stack.Len() < 2 {
+					fmt.Println("stack too small, can't swap")
+				} else {
+					c.stack.Backup()
+					c.stack.Swap()
+				}
+			},
+		),
+
+		"undo": NewCommand(
+			"undo last operation",
+			func(c *Calc) {
+				c.stack.Restore()
+			},
+		),
+
+		"dup": NewCommand(
+			"duplicate last stack item",
+			func(c *Calc) {
+				item := c.stack.Last()
+				if len(item) == 1 {
+					c.stack.Backup()
+					c.stack.Push(item[0])
+				} else {
+					fmt.Println("stack empty")
+				}
+			},
+		),
+	}
+
+	// general commands
+	c.Commands = Commands{
+		"exit": NewCommand(
+			"exit program",
+			func(c *Calc) {
+				os.Exit(0)
+			},
+		),
+
+		"manual": NewCommand(
+			"show manual",
+			func(c *Calc) {
+				man()
+			},
+		),
+	}
+
+	// aliases
+	c.Commands["quit"] = c.Commands["exit"]
+	c.SettingsCommands["undebug"] = c.SettingsCommands["nodebug"]
+	c.SettingsCommands["show"] = c.SettingsCommands["showstack"]
+}

demo/Makefile

@@ -0,0 +1,7 @@
+#
+
+
+all:
+	asciinema rec --cols 80 --row 25 -c "env - PS1='> ' PATH=..:$PATH /bin/bash --norc --noprofile" --overwrite demo.cast
+	agg demo.cast demo.gif
+

demo/demo.cast

@@ -0,0 +1,3 @@
+{"version": 2, "width": 80, "height": 25, "timestamp": 1699358215, "env": {"SHELL": "/bin/bash", "TERM": "tmux-256color"}}
+[0.005628, "o", "> "]
+[0.941195, "o", "exit\r\n"]

demo/sessions.txt

@@ -0,0 +1,18 @@
+# demo sessions, used to create an interactive rpn recording
+
+# part 1: interactive
+
+# put some numbers onto the stack
+2 4 6
+8
+10
+
+# take a look at the stack
+dump
+
+# add the last 2
++
+
+# multiply the result and the previous
+*
+

example.lua

@@ -0,0 +1,38 @@
+-- simple function, return the lower number of the two operands
+function lower(a,b)
+    if a < b then
+        return a
+    else
+        return b
+    end
+end
+
+-- calculate parallel resistance. Batch  function (registered with -1,
+-- see below). Takes a table as parameter.
+--
+-- Formula: 1/( (1/R1) + (1/R2) + ...)
+function parallelresistance(list)
+    sumres = 0
+    
+    for i, value in ipairs(list) do
+        sumres = sumres + 1 / value
+    end
+
+    return 1 / sumres
+end
+
+-- converter example
+function inch2centimeter(inches)
+    return inches * 2.54
+end
+
+function init()
+    -- expects 2 args
+    register("lower", 2, "lower")
+
+    -- expects a list of all numbers on the stack, batch mode
+    register("parallelresistance", -1, "parallel resistance")
+
+    -- expects 1 arg, but doesn't pop()
+    register("inch2centimeter", 0)
+end  

funcs.go

@@ -0,0 +1,460 @@
+/*
+Copyright © 2023 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package main
+
+import (
+	"errors"
+	"math"
+)
+
+type R struct {
+	Res float64
+	Err error
+}
+
+type Numbers []float64
+
+type Function func(Numbers) R
+
+// every function we  are able to call must be  of type Funcall, which
+// needs to  specify how  many numbers  it expects  and the  actual go
+// function to be executed.
+//
+// The function  has to take  a float slice  as argument and  return a
+// float and  an error object. The  float slice is guaranteed  to have
+// the expected number of arguments.
+//
+// However, Lua functions are handled differently, see interpreter.go.
+type Funcall struct {
+	Expectargs int // -1 means batch only mode, you'll get the whole stack as arg
+	Func       Function
+}
+
+// will hold all hard coded functions and operators
+type Funcalls map[string]*Funcall
+
+// convenience function,  create a  new Funcall object,  if expectargs
+// was not specified, 2 is assumed.
+func NewFuncall(function Function, expectargs ...int) *Funcall {
+	expect := 2
+
+	if len(expectargs) > 0 {
+		expect = expectargs[0]
+	}
+
+	return &Funcall{
+		Expectargs: expect,
+		Func:       function,
+	}
+}
+
+// Convenience function, create new result
+func NewR(n float64, e error) R {
+	return R{Res: n, Err: e}
+}
+
+// the actual functions, called once during initialization.
+func DefineFunctions() Funcalls {
+	f := map[string]*Funcall{
+		// simple operators, they all expect 2 args
+		"+": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(arg[0]+arg[1], nil)
+			},
+		),
+
+		"-": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(arg[0]-arg[1], nil)
+			},
+		),
+
+		"x": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(arg[0]*arg[1], nil)
+			},
+		),
+
+		"/": NewFuncall(
+			func(arg Numbers) R {
+				if arg[1] == 0 {
+					return NewR(0, errors.New("division by null"))
+				}
+
+				return NewR(arg[0]/arg[1], nil)
+			},
+		),
+
+		"^": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Pow(arg[0], arg[1]), nil)
+			},
+		),
+
+		"%": NewFuncall(
+			func(arg Numbers) R {
+				return NewR((arg[0]/100)*arg[1], nil)
+			},
+		),
+
+		"%-": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(arg[0]-((arg[0]/100)*arg[1]), nil)
+			},
+		),
+
+		"%+": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(arg[0]+((arg[0]/100)*arg[1]), nil)
+			},
+		),
+
+		"mod": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Remainder(arg[0], arg[1]), nil)
+			},
+		),
+
+		"sqrt": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Sqrt(arg[0]), nil)
+			},
+			1),
+
+		"abs": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Abs(arg[0]), nil)
+			},
+			1),
+
+		"acos": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Acos(arg[0]), nil)
+			},
+			1),
+
+		"acosh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Acosh(arg[0]), nil)
+			},
+			1),
+
+		"asin": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Asin(arg[0]), nil)
+			},
+			1),
+
+		"asinh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Asinh(arg[0]), nil)
+			},
+			1),
+
+		"atan": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Atan(arg[0]), nil)
+			},
+			1),
+
+		"atan2": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Atan2(arg[0], arg[1]), nil)
+			},
+			2),
+
+		"atanh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Atanh(arg[0]), nil)
+			},
+			1),
+
+		"cbrt": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Cbrt(arg[0]), nil)
+			},
+			1),
+
+		"ceil": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Ceil(arg[0]), nil)
+			},
+			1),
+
+		"cos": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Cos(arg[0]), nil)
+			},
+			1),
+
+		"cosh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Cosh(arg[0]), nil)
+			},
+			1),
+
+		"erf": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Erf(arg[0]), nil)
+			},
+			1),
+
+		"erfc": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Erfc(arg[0]), nil)
+			},
+			1),
+
+		"erfcinv": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Erfcinv(arg[0]), nil)
+			},
+			1),
+
+		"erfinv": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Erfinv(arg[0]), nil)
+			},
+			1),
+
+		"exp": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Exp(arg[0]), nil)
+			},
+			1),
+
+		"exp2": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Exp2(arg[0]), nil)
+			},
+			1),
+
+		"expm1": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Expm1(arg[0]), nil)
+			},
+			1),
+
+		"floor": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Floor(arg[0]), nil)
+			},
+			1),
+
+		"gamma": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Gamma(arg[0]), nil)
+			},
+			1),
+
+		"ilogb": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(float64(math.Ilogb(arg[0])), nil)
+			},
+			1),
+
+		"j0": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.J0(arg[0]), nil)
+			},
+			1),
+
+		"j1": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.J1(arg[0]), nil)
+			},
+			1),
+
+		"log": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Log(arg[0]), nil)
+			},
+			1),
+
+		"log10": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Log10(arg[0]), nil)
+			},
+			1),
+
+		"log1p": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Log1p(arg[0]), nil)
+			},
+			1),
+
+		"log2": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Log2(arg[0]), nil)
+			},
+			1),
+
+		"logb": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Logb(arg[0]), nil)
+			},
+			1),
+
+		"pow": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Pow(arg[0], arg[1]), nil)
+			},
+			2),
+
+		"round": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Round(arg[0]), nil)
+			},
+			1),
+
+		"roundtoeven": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.RoundToEven(arg[0]), nil)
+			},
+			1),
+
+		"sin": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Sin(arg[0]), nil)
+			},
+			1),
+
+		"sinh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Sinh(arg[0]), nil)
+			},
+			1),
+
+		"tan": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Tan(arg[0]), nil)
+			},
+			1),
+
+		"tanh": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Tanh(arg[0]), nil)
+			},
+			1),
+
+		"trunc": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Trunc(arg[0]), nil)
+			},
+			1),
+
+		"y0": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Y0(arg[0]), nil)
+			},
+			1),
+
+		"y1": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Y1(arg[0]), nil)
+			},
+			1),
+
+		"copysign": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Copysign(arg[0], arg[1]), nil)
+			},
+			2),
+
+		"dim": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Dim(arg[0], arg[1]), nil)
+			},
+			2),
+
+		"hypot": NewFuncall(
+			func(arg Numbers) R {
+				return NewR(math.Hypot(arg[0], arg[1]), nil)
+			},
+			2),
+	}
+
+	// aliases
+	f["*"] = f["x"]
+	f["remainder"] = f["mod"]
+
+	return f
+}
+
+func DefineBatchFunctions() Funcalls {
+	f := map[string]*Funcall{
+		"median": NewFuncall(
+			func(args Numbers) R {
+				middle := len(args) / 2
+				return NewR(args[middle], nil)
+			},
+			-1),
+
+		"mean": NewFuncall(
+			func(args Numbers) R {
+				var sum float64
+				for _, item := range args {
+					sum += item
+				}
+				return NewR(sum/float64(len(args)), nil)
+			},
+			-1),
+
+		"min": NewFuncall(
+			func(args Numbers) R {
+				var min float64
+				min, args = args[0], args[1:]
+				for _, item := range args {
+					if item < min {
+						min = item
+					}
+				}
+				return NewR(min, nil)
+			},
+			-1),
+
+		"max": NewFuncall(
+			func(args Numbers) R {
+				var max float64
+				max, args = args[0], args[1:]
+				for _, item := range args {
+					if item > max {
+						max = item
+					}
+				}
+				return NewR(max, nil)
+			},
+			-1),
+
+		"sum": NewFuncall(
+			func(args Numbers) R {
+				var sum float64
+				for _, item := range args {
+					sum += item
+				}
+				return NewR(sum, nil)
+			},
+			-1),
+	}
+
+	// aliases
+	f["+"] = f["sum"]
+	f["avg"] = f["mean"]
+
+	return f
+}

interpreter.go

@@ -25,7 +25,8 @@ import (
 )
 
 type Interpreter struct {
-	debug bool
+	debug  bool
+	script string
 }
 
 // LUA interpreter, instanciated in main()
@@ -42,8 +43,12 @@ type LuaFunction struct {
 // have access to the interpreter instance
 var LuaFuncs map[string]LuaFunction
 
+func NewInterpreter(script string, debug bool) *Interpreter {
+	return &Interpreter{debug: debug, script: script}
+}
+
 // initialize the lua environment properly
-func InitLua(config string, debug bool) *Interpreter {
+func (i *Interpreter) InitLua() {
 	// we only  load a subset of lua Open  modules and don't allow
 	// net, system or io stuff
 	for _, pair := range []struct {
@@ -66,7 +71,7 @@ func InitLua(config string, debug bool) *Interpreter {
 	}
 
 	// load the lua config (which we expect to contain init() and math functions)
-	if err := L.DoFile(config); err != nil {
+	if err := L.DoFile(i.script); err != nil {
 		panic(err)
 	}
 
@@ -84,8 +89,6 @@ func InitLua(config string, debug bool) *Interpreter {
 	}); err != nil {
 		panic(err)
 	}
-
-	return &Interpreter{debug: debug}
 }
 
 func (i *Interpreter) Debug(msg string) {
@@ -113,6 +116,8 @@ func (i *Interpreter) CallLuaFunc(funcname string, items []float64) (float64, er
 		funcname, LuaFuncs[funcname].numargs))
 
 	switch LuaFuncs[funcname].numargs {
+	case 0:
+		fallthrough
 	case 1:
 		// 1 arg variant
 		if err := L.CallByParam(lua.P{

main.go

@@ -30,18 +30,20 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.0"
+const VERSION string = "2.0.9"
 
 const Usage string = `This is rpn, a reverse polish notation calculator cli.
 
 Usage: rpn [-bdvh] [<operator>]
 
 Options:
-  -b, --batchmode   enable batch mode
+  -b, --batchmode     enable batch mode
-  -d, --debug       enable debug mode
+  -d, --debug         enable debug mode
-  -m, --manual      show manual
+  -s, --stack         show last 5 items of the stack (off by default)
-  -v, --version     show version
+  -i  --intermediate  print intermediate results
-  -h, --help        show help
+  -m, --manual        show manual
+  -v, --version       show version
+  -h, --help          show help
 
 When <operator>  is given, batch  mode ist automatically  enabled. Use
 this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
@@ -58,6 +60,9 @@ func main() {
 	configfile := ""
 
 	flag.BoolVarP(&calc.batch, "batchmode", "b", false, "batch mode")
+	flag.BoolVarP(&calc.showstack, "show-stack", "s", false, "show stack")
+	flag.BoolVarP(&calc.intermediate, "showin-termediate", "i", false,
+		"show intermediate results")
 	flag.BoolVarP(&enabledebug, "debug", "d", false, "debug mode")
 	flag.BoolVarP(&showversion, "version", "v", false, "show version")
 	flag.BoolVarP(&showhelp, "help", "h", false, "show usage")
@@ -93,8 +98,9 @@ func main() {
 	// our config file is interpreted  as lua code, only functions can
 	// be defined, init() will be called by InitLua().
 	if _, err := os.Stat(configfile); err == nil {
-		I := InitLua(configfile, enabledebug)
+		luarunner := NewInterpreter(configfile, enabledebug)
-		calc.SetInt(I)
+		luarunner.InitLua()
+		calc.SetInt(luarunner)
 	}
 
 	if len(flag.Args()) > 1 {

rpn.go

@@ -2,16 +2,19 @@ package main
 
 var manpage = `
 NAME
-    rpn - Reverse Polish Notation Calculator for the commandline
+    rpn - Programmable command-line calculator using reverse polish notation
 
 SYNOPSIS
         Usage: rpn [-bdvh] [<operator>]
     
         Options:
-          -b, --batchmode   enable batch mode
+          -b, --batchmode     enable batch mode
-          -d, --debug       enable debug mode
+          -d, --debug         enable debug mode
-          -v, --version     show version
+          -s, --stack         show last 5 items of the stack (off by default)
-          -h, --help        show help
+          -i  --intermediate  print intermediate results
+          -m, --manual        show manual
+          -v, --version       show version
+          -h, --help          show help
     
         When <operator>  is given, batch  mode ist automatically  enabled. Use
         this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
@@ -111,25 +114,110 @@ DESCRIPTION
     switch or debug toggle command), then the backup stack is also being
     displayed.
 
-    The stack can be reversed using the reverse command.
+    The stack can be reversed using the reverse command. However, sometimes
+    only the last two values are in the wrong order. Use the swap command to
+    exchange them.
 
     You can use the shift command to remove the last number from the stack.
 
   BUILTIN OPERATORS AND FUNCTIONS
-    Basic operators: + - x /
+    Basic operators:
 
-    Math functions:
+        +                    add
+        -                    substract
+        /                    divide
+        x                    multiply (alias: *)
+        ^                    power
+
+    Percent functions:
 
-        sqrt                 square root
-        mod                  remainder of division (alias: remainder)
-        max                  batch mode only: max of all values
-        min                  batch mode only: min of all values
-        mean                 batch mode only: mean of all values (alias: avg)
-        median               batch mode only: median of all values
         %                    percent
         %-                   substract percent
         %+                   add percent
-        ^                    power
+
+    Batch functions:
+
+        sum                  sum of all values (alias: +)
+        max                  max of all values
+        min                  min of all values
+        mean                 mean of all values (alias: avg)
+        median               median of all values
+
+    Math functions:
+
+        mod sqrt abs acos acosh asin asinh atan atan2 atanh cbrt ceil cos cosh
+        erf erfc  erfcinv erfinv exp  exp2 expm1 floor  gamma ilogb j0  j1 log
+        log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
+        y1 copysign dim hypot
+
+    Commands:
+
+        [no]batch            toggle batch mode (nobatch turns it off)
+        [no]debug            toggle debug output (nodebug turns it off)
+        [no]showstack        show the last 5 items of the stack (noshowtack turns it off)
+        dump                 display the stack contents
+        clear                clear the whole stack
+        shift                remove the last element of the stack
+        reverse              reverse the stack elements
+        swap                 exchange the last two stack elements
+        dup                  duplicate last stack item
+        history              display calculation history
+        help|?               show this message
+        quit|exit|c-d|c-c    exit program
+
+    Register variables:
+
+        >NAME                Put last stack element into variable NAME
+        <NAME                Retrieve variable NAME and put onto stack
+
+    Refer to https://pkg.go.dev/math for details about those functions.
+
+INTERACTIVE REPL
+    While you can use rpn in the command-line, the best experience you'll
+    have is the interactive repl (read eval print loop). Just execute "rpn"
+    and you'll be there.
+
+    In interactive mode you can use TAB completion to complete commands,
+    operators and functions. There's also a history, which allows you to
+    repeat complicated calculations (as long as you've entered them in one
+    line).
+
+    There are also a lot of key bindings, here are the most important ones:
+
+    ctrl-c + ctrl-d
+        Exit interactive rpn
+
+    ctrl-z
+        Send rpn to the backgound.
+
+    ctrl-a
+        Beginning of line.
+
+    ctrl-e
+        End of line.
+
+    ctrl-l
+        Clear the screen.
+
+    ctrl-r
+        Search through history.
+
+COMMENTS
+    Lines starting with "#" are being ignored as comments. You can also
+    append comments to rpn input, e.g.:
+
+       # a comment
+       123   # another comment
+
+    In this case only 123 will be added to the stack.
+
+VARIABLES
+    You can register the last item of the stack into a variable. Variable
+    names must be all caps. Use the ">NAME" command to put a value into
+    variable "NAME". Use "<NAME" to retrieve the value of variable "NAME"
+    and put it onto the stack.
+
+    The command vars can be used to get a list of all variables.
 
 EXTENDING RPN USING LUA
     You can use a lua script with lua functions to extend the calculator. By
@@ -157,8 +245,13 @@ EXTENDING RPN USING LUA
 
     *   function name
 
-    *   number of arguments expected (1,2 or -1 allowed), -1 means batch
+    *   number of arguments expected (see below)
-        mode.
+
+        Number of expected arguments can be:
+
+            - 0: expect 1 argument but do NOT modify the stack
+            - 1-n: do a singular calculation
+            - -1: batch mode work with all numbers on the stack
 
     *   help text
 
@@ -206,17 +299,3 @@ AUTHORS
     Thomas von Dein tom AT vondein DOT org
 
 `
-var usage = `
-
-Usage: rpn [-bdvh] [<operator>]
-
-Options:
-  -b, --batchmode   enable batch mode
-  -d, --debug       enable debug mode
-  -v, --version     show version
-  -h, --help        show help
-
-When <operator>  is given, batch  mode ist automatically  enabled. Use
-this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
-
-`

rpn.pod

@@ -1,16 +1,19 @@
 =head1 NAME 
 
-rpn - Reverse Polish Notation Calculator for the commandline
+rpn - Programmable command-line calculator using reverse polish notation
 
 =head1 SYNOPSIS
 
     Usage: rpn [-bdvh] [<operator>]
     
     Options:
-      -b, --batchmode   enable batch mode
+      -b, --batchmode     enable batch mode
-      -d, --debug       enable debug mode
+      -d, --debug         enable debug mode
-      -v, --version     show version
+      -s, --stack         show last 5 items of the stack (off by default)
-      -h, --help        show help
+      -i  --intermediate  print intermediate results
+      -m, --manual        show manual
+      -v, --version       show version
+      -h, --help          show help
     
     When <operator>  is given, batch  mode ist automatically  enabled. Use
     this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +
@@ -116,27 +119,127 @@ You can use B<dump> to display the stack. If debugging
 is enabled (C<-d> switch or B<debug> toggle command), then the backup
 stack is also being displayed.
 
-The stack can be reversed using the B<reverse> command.
+The  stack can  be  reversed using  the  B<reverse> command.  However,
+sometimes only  the last two  values are in  the wrong order.  Use the
+B<swap> command to exchange them.
 
 You can use the B<shift> command to remove the last number from the
 stack.
 
 =head2 BUILTIN OPERATORS AND FUNCTIONS
 
-Basic operators: + - x /
+Basic operators:
 
-Math functions:
+    +                    add
+    -                    substract
+    /                    divide
+    x                    multiply (alias: *)
+    ^                    power
+
+Percent functions:
 
-    sqrt                 square root
-    mod                  remainder of division (alias: remainder)
-    max                  batch mode only: max of all values
-    min                  batch mode only: min of all values
-    mean                 batch mode only: mean of all values (alias: avg)
-    median               batch mode only: median of all values
     %                    percent
     %-                   substract percent
     %+                   add percent
-    ^                    power
+
+Batch functions:
+
+    sum                  sum of all values (alias: +)
+    max                  max of all values
+    min                  min of all values
+    mean                 mean of all values (alias: avg)
+    median               median of all values
+
+Math functions:
+
+    mod sqrt abs acos acosh asin asinh atan atan2 atanh cbrt ceil cos cosh
+    erf erfc  erfcinv erfinv exp  exp2 expm1 floor  gamma ilogb j0  j1 log
+    log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
+    y1 copysign dim hypot
+
+Commands:
+
+    [no]batch            toggle batch mode (nobatch turns it off)
+    [no]debug            toggle debug output (nodebug turns it off)
+    [no]showstack        show the last 5 items of the stack (noshowtack turns it off)
+    dump                 display the stack contents
+    clear                clear the whole stack
+    shift                remove the last element of the stack
+    reverse              reverse the stack elements
+    swap                 exchange the last two stack elements
+    dup                  duplicate last stack item
+    history              display calculation history
+    help|?               show this message
+    quit|exit|c-d|c-c    exit program
+
+
+Register variables:
+
+    >NAME                Put last stack element into variable NAME
+    <NAME                Retrieve variable NAME and put onto stack
+
+Refer to https://pkg.go.dev/math for details about those functions.
+
+=head1 INTERACTIVE REPL
+
+While you can use rpn in the command-line, the best experience you'll
+have is the interactive repl (read eval print loop). Just execute
+C<rpn> and you'll be there.
+
+In interactive mode you can use TAB completion to complete commands,
+operators and functions. There's also a history, which allows you to
+repeat complicated calculations (as long as you've entered them in one
+line).
+
+There are also a lot of key bindings, here are the most important
+ones:
+
+=over
+
+=item ctrl-c + ctrl-d
+
+Exit interactive rpn
+
+=item ctrl-z
+
+Send rpn to the backgound.
+
+=item ctrl-a
+
+Beginning of line.
+
+=item ctrl-e
+
+End of line.
+
+=item ctrl-l
+
+Clear the screen.
+
+=item ctrl-r
+
+Search through history.
+
+=back
+
+=head1 COMMENTS
+
+Lines starting with  C<#> are being ignored as comments.  You can also
+append comments to rpn input, e.g.:
+
+   # a comment
+   123   # another comment
+
+In this case only 123 will be added to the stack.
+
+=head1 VARIABLES
+
+You can register the last item  of the stack into a variable. Variable
+names must be  all caps. Use the  ">NAME" command to put  a value into
+variable "NAME". Use "<NAME" to  retrieve the value of variable "NAME"
+and put it onto the stack.
+
+The command B<vars> can be used to get a list of all variables.
 
 =head1 EXTENDING RPN USING LUA
 
@@ -171,8 +274,13 @@ function name
 
 =item *
 
-number of arguments expected (1,2 or -1 allowed), -1 means batch
+number of arguments expected (see below)
-mode.
+
+Number of expected arguments can be:
+
+    - 0: expect 1 argument but do NOT modify the stack
+    - 1-n: do a singular calculation
+    - -1: batch mode work with all numbers on the stack 
 
 =item *
 

stack.go

@@ -94,46 +94,63 @@ func (s *Stack) Pop() float64 {
 }
 
 // just remove the last item, do not return it
-func (s *Stack) Shift() {
+func (s *Stack) Shift(num ...int) {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
+	count := 1
+
+	if len(num) > 0 {
+		count = num[0]
+	}
+
 	if s.linklist.Len() == 0 {
 		return
 	}
 
-	tail := s.linklist.Back()
+	for i := 0; i < count; i++ {
-	s.linklist.Remove(tail)
+		tail := s.linklist.Back()
-
+		s.linklist.Remove(tail)
-	s.Debug(fmt.Sprintf("remove from stack: %.2f", tail.Value))
+		s.Debug(fmt.Sprintf("remove from stack: %.2f", tail.Value))
+	}
 }
 
-// just return the last item, do not remove it
+func (s *Stack) Swap() {
-func (s *Stack) Last() float64 {
+	s.mutex.Lock()
-	if s.linklist.Back() == nil {
+	defer s.mutex.Unlock()
-		return 0
+
+	if s.linklist.Len() < 2 {
+		return
 	}
 
-	return s.linklist.Back().Value.(float64)
+	a := s.linklist.Back()
+	s.linklist.Remove(a)
+
+	b := s.linklist.Back()
+	s.linklist.Remove(b)
+
+	s.Debug(fmt.Sprintf("swapping %.2f with %.2f", b.Value, a.Value))
+
+	s.linklist.PushBack(a.Value)
+	s.linklist.PushBack(b.Value)
 }
 
-// Return the last 2 elements of the stack without modifying it.
+// Return the last num items from the stack w/o modifying it.
-//
+func (s *Stack) Last(num ...int) []float64 {
-// We  need to return  the last 2  elements of the  stack, however
-// container/list only  supports access to 1 last  element. So, we
-// pop the last, retrieve the  second last and push the popped one
-// back.
-func (s *Stack) LastTwo() []float64 {
 	items := []float64{}
-	if s.linklist.Back() == nil {
+	i := s.Len()
-		return items
+	count := 1
+	if len(num) > 0 {
+		count = num[0]
 	}
 
-	last := s.Pop()
+	for e := s.linklist.Front(); e != nil; e = e.Next() {
-	items = append(items, last)
+		if i <= count {
-	items = append(items, s.linklist.Back().Value.(float64))
+			items = append(items, e.Value.(float64))
+		}
+		i--
+	}
 
-	s.Push(last)
 	return items
 }
 
@@ -164,7 +181,7 @@ func (s *Stack) Dump() {
 }
 
 func (s *Stack) Clear() {
-	s.Debug("DEBUG: clearing stack")
+	s.Debug("clearing stack")
 
 	s.linklist = list.List{}
 }
@@ -178,14 +195,24 @@ func (s *Stack) Backup() {
 	// make a backup, because the elements in list.List{} are pointers
 	// and lead to unexpected  results. The methid here works reliably
 	// at least.
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	s.Debug(fmt.Sprintf("backing up %d items from rev %d",
+		s.linklist.Len(), s.rev))
+
 	s.backup = list.List{}
 	for e := s.linklist.Front(); e != nil; e = e.Next() {
-		s.backup.PushBack(e.Value)
+		s.backup.PushBack(e.Value.(float64))
 	}
+
 	s.backuprev = s.rev
 }
 
 func (s *Stack) Restore() {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
 	if s.rev == 0 {
 		fmt.Println("error: stack is empty.")
 		return
@@ -194,15 +221,26 @@ func (s *Stack) Restore() {
 	s.Debug(fmt.Sprintf("restoring stack to revision %d", s.backuprev))
 
 	s.rev = s.backuprev
-	s.linklist = s.backup
+
+	s.linklist = list.List{}
+	for e := s.backup.Front(); e != nil; e = e.Next() {
+		s.linklist.PushBack(e.Value.(float64))
+	}
 }
 
 func (s *Stack) Reverse() {
-	newstack := list.List{}
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	items := []float64{}
 
 	for e := s.linklist.Front(); e != nil; e = e.Next() {
-		newstack.PushFront(e.Value)
+		tail := s.linklist.Back()
+		items = append(items, tail.Value.(float64))
+		s.linklist.Remove(tail)
 	}
 
-	s.linklist = newstack
+	for i := len(items) - 1; i >= 0; i-- {
+		s.linklist.PushFront(items[i])
+	}
 }

stack_test.go

@@ -0,0 +1,190 @@
+/*
+Copyright © 2023 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package main
+
+import (
+	"testing"
+)
+
+func TestPush(t *testing.T) {
+	t.Run("push", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+
+		if s.linklist.Back().Value != 5.0 {
+			t.Errorf("push failed:\n+++  got: %f\n--- want: %f",
+				s.linklist.Back().Value, 5.0)
+		}
+	})
+}
+
+func TestPop(t *testing.T) {
+	t.Run("pop", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+		got := s.Pop()
+
+		if got != 5.0 {
+			t.Errorf("pop failed:\n+++  got: %f\n--- want: %f",
+				got, 5.0)
+		}
+
+		if s.Len() != 0 {
+			t.Errorf("stack not empty after pop()")
+		}
+	})
+}
+
+func TestPops(t *testing.T) {
+	t.Run("pops", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+		s.Push(5)
+		s.Push(5)
+		s.Pop()
+
+		if s.Len() != 2 {
+			t.Errorf("stack len not correct after pop:\n+++  got: %d\n--- want: %d",
+				s.Len(), 2)
+		}
+	})
+}
+
+func TestShift(t *testing.T) {
+	t.Run("shift", func(t *testing.T) {
+		s := NewStack()
+		s.Shift()
+
+		if s.Len() != 0 {
+			t.Errorf("stack not empty after shift()")
+		}
+	})
+}
+
+func TestClear(t *testing.T) {
+	t.Run("clear", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+		s.Push(5)
+		s.Push(5)
+		s.Clear()
+
+		if s.Len() != 0 {
+			t.Errorf("stack not empty after clear()")
+		}
+	})
+}
+
+func TestLast(t *testing.T) {
+	t.Run("last", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+		got := s.Last()
+
+		if len(got) != 1 {
+			t.Errorf("last failed:\n+++  got: %d elements\n--- want: %d elements",
+				len(got), 1)
+		}
+
+		if got[0] != 5.0 {
+			t.Errorf("last failed:\n+++  got: %f\n--- want: %f",
+				got, 5.0)
+		}
+
+		if s.Len() != 1 {
+			t.Errorf("stack modified after last()")
+		}
+	})
+}
+
+func TestAll(t *testing.T) {
+	t.Run("all", func(t *testing.T) {
+		s := NewStack()
+		list := []float64{2, 4, 6, 8}
+
+		for _, item := range list {
+			s.Push(item)
+		}
+
+		got := s.All()
+
+		if len(got) != len(list) {
+			t.Errorf("all failed:\n+++  got: %d elements\n--- want: %d elements",
+				len(got), len(list))
+		}
+
+		for i := 1; i < len(list); i++ {
+			if got[i] != list[i] {
+				t.Errorf("all failed (element %d):\n+++  got: %f\n--- want: %f",
+					i, got[i], list[i])
+			}
+		}
+
+		if s.Len() != len(list) {
+			t.Errorf("stack modified after last()")
+		}
+	})
+}
+
+func TestBackupRestore(t *testing.T) {
+	t.Run("shift", func(t *testing.T) {
+		s := NewStack()
+		s.Push(5)
+		s.Backup()
+		s.Clear()
+		s.Restore()
+
+		if s.Len() != 1 {
+			t.Errorf("stack not correctly restored()")
+		}
+
+		a := s.Pop()
+		if a != 5.0 {
+			t.Errorf("stack not identical to old revision:\n+++  got: %f\n--- want: %f",
+				a, 5.0)
+		}
+	})
+}
+
+func TestReverse(t *testing.T) {
+	t.Run("reverse", func(t *testing.T) {
+		s := NewStack()
+		list := []float64{2, 4, 6}
+		reverse := []float64{6, 4, 2}
+
+		for _, item := range list {
+			s.Push(item)
+		}
+
+		s.Reverse()
+
+		got := s.All()
+
+		if len(got) != len(list) {
+			t.Errorf("all failed:\n+++  got: %d elements\n--- want: %d elements",
+				len(got), len(list))
+		}
+
+		for i := 1; i < len(reverse); i++ {
+			if got[i] != reverse[i] {
+				t.Errorf("reverse failed (element %d):\n+++  got: %f\n--- want: %f",
+					i, got[i], list[i])
+			}
+		}
+	})
+}

test.lua

@@ -1,17 +0,0 @@
-function add(a,b)
-  return a + b
-end
-
-function test(a)
-  return a
-end  
-
-function parallelresistance(a,b)
-  return 1.0 / (a * b)
-end
-
-function init()
-  register("add", 2, "addition")
-  register("test", 1, "test")
-  register("parallelresistance", 2, "parallel resistance")
-end  

util.go

@@ -17,7 +17,11 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 package main
 
-import "math"
+import (
+	"fmt"
+	"math"
+	"strings"
+)
 
 // find an item in a list
 func contains(s []string, e string) bool {
@@ -55,3 +59,7 @@ func const2num(name string) float64 {
 		return 0
 	}
 }
+
+func list2str(list Numbers) string {
+	return strings.Trim(strings.Join(strings.Fields(fmt.Sprint(list)), " "), "[]")
+}

util_test.go

@@ -0,0 +1,32 @@
+/*
+Copyright © 2023 Thomas von Dein
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package main
+
+import (
+	"testing"
+)
+
+func TestContains(t *testing.T) {
+	list := []string{"a", "b", "c"}
+
+	t.Run("contains", func(t *testing.T) {
+		if !contains(list, "a") {
+			t.Errorf("a in [a,b,c] not found")
+		}
+	})
+}