add variable support, implements #10 (#14)

* add interactiveness to features, add keybindings to doc
* added commands

.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"
-	go test -run $(TEST) github.com/tlinden/rpn/$(MOD)
+	@echo "Call like this: ''make singletest TEST=TestPrepareColumns"
+	go test -run $(TEST)
 
 cover-report:
 	go test ./... -cover -coverprofile=coverage.out
@@ -77,3 +72,15 @@ buildall:
 
 release: buildall
 	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

calc.go

@@ -20,7 +20,6 @@ package main
 import (
 	"errors"
 	"fmt"
-	"math"
 	"os"
 	"regexp"
 	"strconv"
@@ -33,25 +32,36 @@ type Calc struct {
 	debug        bool
 	batch        bool
 	stdin        bool
+	showstack    bool
+	intermediate bool
+	notdone      bool // set to true as long as there are items left in the eval loop
 	stack        *Stack
 	history      []string
 	completer    readline.AutoCompleter
 	interpreter  *Interpreter
 	Space        *regexp.Regexp
+	Comment      *regexp.Regexp
+	Register     *regexp.Regexp
 	Constants    []string
 	LuaFunctions []string
 
 	Funcalls      Funcalls
 	BatchFuncalls Funcalls
+
+	Vars map[string]float64
 }
 
 // help for lua functions will be added dynamically
 const Help string = `Available commands:
 batch                toggle batch mode
 debug                toggle debug output
+show                 show the last 5 items of the stack
 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 elements
+vars                 show list of variables
 history              display calculation history
 help|?               show this message
 quit|exit|c-d|c-c    exit program
@@ -75,12 +85,16 @@ 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`
+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 debug undebug clear batch shift undo help history manual exit quit swap show vars`
 	Constants string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
 )
 
@@ -122,6 +136,7 @@ func NewCalc() *Calc {
 
 	c.Funcalls = DefineFunctions()
 	c.BatchFuncalls = DefineBatchFunctions()
+	c.Vars = map[string]float64{}
 
 	c.completer = readline.NewPrefixCompleter(
 		// custom lua functions
@@ -130,6 +145,8 @@ func NewCalc() *Calc {
 	)
 
 	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, " ")
@@ -161,14 +178,21 @@ 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)
@@ -179,33 +203,28 @@ 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 contains(c.MathFunctions, item) {
-					// go builtin math function, if implemented
-					c.mathfunc(item)
-					continue
-				}
-
-				if contains(c.BatchFunctions, item) {
-					// math functions only supported in batch mode like max or mean
-					c.batchfunc(item)
-					continue
-				}
-			*/
-
 			if contains(c.Constants, item) {
 				// put the constant onto the stack
 				c.stack.Backup()
@@ -244,15 +263,28 @@ func (c *Calc) Eval(line string) {
 				continue
 			}
 
+			regmatches := c.Register.FindStringSubmatch(item)
+			if len(regmatches) == 3 {
+				switch regmatches[1] {
+				case ">":
+					c.PutVar(regmatches[2])
+				case "<":
+					c.GetVar(regmatches[2])
+				}
+				continue
+			}
+
 			// management commands
 			switch item {
 			case "?":
 				fallthrough
 			case "help":
 				fmt.Println(Help)
-				fmt.Println("Lua functions:")
-				for name, function := range LuaFuncs {
-					fmt.Printf("%-20s %s\n", name, function.help)
+				if len(LuaFuncs) > 0 {
+					fmt.Println("Lua functions:")
+					for name, function := range LuaFuncs {
+						fmt.Printf("%-20s %s\n", name, function.help)
+					}
 				}
 			case "dump":
 				c.stack.Dump()
@@ -271,23 +303,52 @@ func (c *Calc) Eval(line string) {
 			case "reverse":
 				c.stack.Backup()
 				c.stack.Reverse()
+			case "swap":
+				if c.stack.Len() < 2 {
+					fmt.Println("stack too small, can't swap")
+				} else {
+					c.stack.Backup()
+					c.stack.Swap()
+				}
 			case "undo":
 				c.stack.Restore()
 			case "history":
 				for _, entry := range c.history {
 					fmt.Println(entry)
 				}
+			case "show":
+				c.ToggleShow()
 			case "exit":
 				fallthrough
 			case "quit":
 				os.Exit(0)
 			case "manual":
 				man()
+			case "vars":
+				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")
+				}
+
 			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
@@ -361,11 +422,16 @@ func (c *Calc) History(format string, args ...any) {
 
 // print the result
 func (c *Calc) Result() float64 {
-	if !c.stdin {
-		fmt.Print("= ")
-	}
+	// we only  print the result if it's either  a final result or
+	// (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()[0])
+	}
 
 	return c.stack.Last()[0]
 }
@@ -376,50 +442,6 @@ func (c *Calc) Debug(msg string) {
 	}
 }
 
-// do simple calculations
-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()
-}
-
 func (c *Calc) luafunc(funcname string) {
 	// called from calc loop
 	var x float64
@@ -460,3 +482,24 @@ func (c *Calc) luafunc(funcname string) {
 
 	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")
+	}
+}

calc_test.go

@@ -0,0 +1,214 @@
+/*
+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"
+)
+
+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
+	}{
+		{
+			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,
+		},
+		{
+			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,
+		},
+		{
+			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,
+		},
+	}
+
+	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)
+			}
+		})
+	}
+}

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
+*
+

main.go

@@ -30,18 +30,20 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.1"
+const VERSION string = "2.0.5"
 
 const Usage string = `This is rpn, a reverse polish notation calculator cli.
 
 Usage: rpn [-bdvh] [<operator>]
 
 Options:
-  -b, --batchmode   enable batch mode
-  -d, --debug       enable debug mode
-  -m, --manual      show manual
-  -v, --version     show version
-  -h, --help        show help
+  -b, --batchmode     enable batch mode
+  -d, --debug         enable debug mode
+  -s, --stack         show last 5 items of the stack (off by default)
+  -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 +
@@ -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")

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
-          -d, --debug       enable debug mode
-          -v, --version     show version
-          -h, --help        show help
+          -b, --batchmode     enable batch mode
+          -d, --debug         enable debug mode
+          -s, --stack         show last 5 items of the stack (off by default)
+          -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 +
@@ -111,7 +114,9 @@ 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.
 
@@ -145,8 +150,75 @@ DESCRIPTION
         log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
         y1 copysign dim hypot
 
+    Commands:
+
+        batch                toggle batch mode
+        debug                toggle debug output
+        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
+        show                 show the last 5 items of the stack
+        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
     default the tool looks for "~/.rpn.lua". You can also specify a script
@@ -222,17 +294,3 @@ 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
-      -d, --debug       enable debug mode
-      -v, --version     show version
-      -h, --help        show help
+      -b, --batchmode     enable batch mode
+      -d, --debug         enable debug mode
+      -s, --stack         show last 5 items of the stack (off by default)
+      -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 +
@@ -116,7 +119,9 @@ 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.
@@ -152,8 +157,89 @@ Math functions:
     log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
     y1 copysign dim hypot
 
+Commands:
+
+    batch                toggle batch mode
+    debug                toggle debug output
+    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
+    show                 show the last 5 items of the stack
+    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
 
 You can use a lua script with lua functions to extend the

stack.go

@@ -115,6 +115,26 @@ func (s *Stack) Shift(num ...int) {
 	}
 }
 
+func (s *Stack) Swap() {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+
+	if s.linklist.Len() < 2 {
+		return
+	}
+
+	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 num items from the stack w/o modifying it.
 func (s *Stack) Last(num ...int) []float64 {
 	items := []float64{}

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])
+			}
+		}
+	})
+}

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")
+		}
+	})
+}