Add demo mp4

* reorganized Eval() to return errors and call EvalItem() on each item
* fix negative shift amount error, found with fuzzy testing :)
* added fuzzy testing

Makefile

@@ -51,14 +51,25 @@ install: buildlocal
 	install -o $(UID) -g $(GID) -m 444 $(tool).1 $(PREFIX)/man/man1/
 
 clean:
-	rm -rf $(tool) coverage.out
+	rm -rf $(tool) coverage.out testdata
 
-test:
-	go test -v ./...
+test: clean
+	go test ./... $(ARGS)
+
+testfuzzy: clean
+	go test -fuzz ./... $(ARGS)
+
+testlint: test lint
+
+lint:
+	golangci-lint run
+
+lint-full:
+	golangci-lint run --enable-all --exclude-use-default --disable exhaustivestruct,exhaustruct,depguard,interfacer,deadcode,golint,structcheck,scopelint,varcheck,ifshort,maligned,nosnakecase,godot,funlen,gofumpt,cyclop,noctx,gochecknoglobals,paralleltest,forbidigo,godox,dupword,forcetypeassert,goerr113,gomnd
 
 singletest:
-	@echo "Call like this: ''make singletest TEST=TestPrepareColumns"
-	go test -run $(TEST)
+	@echo "Call like this: make singletest TEST=TestPrepareColumns ARGS=-v"
+	go test -run $(TEST) $(ARGS)
 
 cover-report:
 	go test ./... -cover -coverprofile=coverage.out

calc.go

@@ -1,5 +1,5 @@
 /*
-Copyright © 2023 Thomas von Dein
+Copyright © 2023-2024 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
@@ -20,6 +20,7 @@ package main
 import (
 	"errors"
 	"fmt"
+	"math"
 	"regexp"
 	"sort"
 	"strconv"
@@ -35,6 +36,8 @@ type Calc struct {
 	showstack    bool
 	intermediate bool
 	notdone      bool // set to true as long as there are items left in the eval loop
+	precision    int
+
 	stack        *Stack
 	history      []string
 	completer    readline.AutoCompleter
@@ -66,7 +69,7 @@ Bitwise operators: and or xor < (left shift) > (right shift)
 
 Percent functions:
 %                    percent
-%-                   substract percent
+%-                   subtract percent
 %+                   add percent
 
 Math functions (see https://pkg.go.dev/math):
@@ -89,8 +92,9 @@ Register variables:
 // commands, constants and operators,  defined here to feed completion
 // and our mode switch in Eval() dynamically
 const (
-	//Commands  string = `dump reverse clear shift undo help history manual exit quit swap debug undebug nodebug batch nobatch showstack noshowstack vars`
-	Constants string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
+	Constants    string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
+	Precision    int    = 2
+	ShowStackLen int    = 5
 )
 
 // That way we can add custom functions to completion
@@ -146,37 +150,36 @@ func (c *Calc) GetCompleteCustomFuncalls() func(string) []string {
 
 		return completions
 	}
-
 }
 
 func NewCalc() *Calc {
-	c := Calc{stack: NewStack(), debug: false}
+	calc := Calc{stack: NewStack(), debug: false, precision: Precision}
 
-	c.Funcalls = DefineFunctions()
-	c.BatchFuncalls = DefineBatchFunctions()
-	c.Vars = map[string]float64{}
+	calc.Funcalls = DefineFunctions()
+	calc.BatchFuncalls = DefineBatchFunctions()
+	calc.Vars = map[string]float64{}
 
-	c.completer = readline.NewPrefixCompleter(
+	calc.completer = readline.NewPrefixCompleter(
 		// custom lua functions
 		readline.PcItemDynamic(GetCompleteCustomFunctions()),
-		readline.PcItemDynamic(c.GetCompleteCustomFuncalls()),
+		readline.PcItemDynamic(calc.GetCompleteCustomFuncalls()),
 	)
 
-	c.Space = regexp.MustCompile(`\s+`)
-	c.Comment = regexp.MustCompile(`#.*`) // ignore everything after #
-	c.Register = regexp.MustCompile(`^([<>])([A-Z][A-Z0-9]*)`)
+	calc.Space = regexp.MustCompile(`\s+`)
+	calc.Comment = regexp.MustCompile(`#.*`) // ignore everything after #
+	calc.Register = regexp.MustCompile(`^([<>])([A-Z][A-Z0-9]*)`)
 
 	// pre-calculate mode switching arrays
-	c.Constants = strings.Split(Constants, " ")
+	calc.Constants = strings.Split(Constants, " ")
 
-	c.SetCommands()
+	calc.SetCommands()
 
-	return &c
+	return &calc
 }
 
 // setup the interpreter, called from main(), import lua functions
-func (c *Calc) SetInt(I *Interpreter) {
-	c.interpreter = I
+func (c *Calc) SetInt(interpreter *Interpreter) {
+	c.interpreter = interpreter
 
 	for name := range LuaFuncs {
 		c.LuaFunctions = append(c.LuaFunctions, name)
@@ -203,31 +206,31 @@ func (c *Calc) ToggleShow() {
 }
 
 func (c *Calc) Prompt() string {
-	p := "\033[31m»\033[0m "
-	b := ""
+	prompt := "\033[31m»\033[0m "
+	batch := ""
 
 	if c.batch {
-		b = "->batch"
+		batch = "->batch"
 	}
 
-	d := ""
-	v := ""
+	debug := ""
+	revision := ""
 
 	if c.debug {
-		d = "->debug"
-		v = fmt.Sprintf("/rev%d", c.stack.rev)
+		debug = "->debug"
+		revision = fmt.Sprintf("/rev%d", c.stack.rev)
 	}
 
-	return fmt.Sprintf("rpn%s%s [%d%s]%s", b, d, c.stack.Len(), v, p)
+	return fmt.Sprintf("rpn%s%s [%d%s]%s", batch, debug, c.stack.Len(), revision, prompt)
 }
 
 // the actual work horse, evaluate a line of calc command[s]
-func (c *Calc) Eval(line string) {
+func (c *Calc) Eval(line string) error {
 	// remove surrounding whitespace and comments, if any
 	line = strings.TrimSpace(c.Comment.ReplaceAllString(line, ""))
 
 	if line == "" {
-		return
+		return nil
 	}
 
 	items := c.Space.Split(line, -1)
@@ -239,112 +242,135 @@ func (c *Calc) Eval(line string) {
 			c.notdone = false
 		}
 
-		num, err := strconv.ParseFloat(item, 64)
-
-		if err == nil {
-			c.stack.Backup()
-			c.stack.Push(num)
-		} else {
-			// try hex
-			var i int
-			_, err := fmt.Sscanf(item, "0x%x", &i)
-			if err == nil {
-				c.stack.Backup()
-				c.stack.Push(float64(i))
-				continue
-			}
-
-			if contains(c.Constants, item) {
-				// put the constant onto the stack
-				c.stack.Backup()
-				c.stack.Push(const2num(item))
-				continue
-			}
-
-			if _, ok := c.Funcalls[item]; ok {
-				if err := c.DoFuncall(item); err != nil {
-					fmt.Println(err)
-				} else {
-					c.Result()
-				}
-				continue
-			}
-
-			if c.batch {
-				if _, ok := c.BatchFuncalls[item]; ok {
-					if err := c.DoFuncall(item); err != nil {
-						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.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
-			}
-
-			switch item {
-			case "?":
-				fallthrough
-			case "help":
-				c.PrintHelp()
-
-			default:
-				fmt.Println("unknown command or operator!")
-			}
+		if err := c.EvalItem(item); err != nil {
+			return err
 		}
 	}
 
 	if c.showstack && !c.stdin {
 		dots := ""
 
-		if c.stack.Len() > 5 {
+		if c.stack.Len() > ShowStackLen {
 			dots = "... "
 		}
-		last := c.stack.Last(5)
+
+		last := c.stack.Last(ShowStackLen)
+
 		fmt.Printf("stack: %s%s\n", dots, list2str(last))
 	}
+
+	return nil
+}
+
+func (c *Calc) EvalItem(item string) error {
+	num, err := strconv.ParseFloat(item, 64)
+
+	if err == nil {
+		c.stack.Backup()
+		c.stack.Push(num)
+
+		return nil
+	}
+
+	// try hex
+	var i int
+
+	_, err = fmt.Sscanf(item, "0x%x", &i)
+	if err == nil {
+		c.stack.Backup()
+		c.stack.Push(float64(i))
+
+		return nil
+	}
+
+	if contains(c.Constants, item) {
+		// put the constant onto the stack
+		c.stack.Backup()
+		c.stack.Push(const2num(item))
+
+		return nil
+	}
+
+	if exists(c.Funcalls, item) {
+		if err := c.DoFuncall(item); err != nil {
+			return Error(err.Error())
+		}
+
+		c.Result()
+
+		return nil
+	}
+
+	if exists(c.BatchFuncalls, item) {
+		if !c.batch {
+			return Error("only supported in batch mode")
+		}
+
+		if err := c.DoFuncall(item); err != nil {
+			return Error(err.Error())
+		}
+
+		c.Result()
+
+		return nil
+	}
+
+	if contains(c.LuaFunctions, item) {
+		// user provided custom lua functions
+		c.EvalLuaFunction(item)
+
+		return nil
+	}
+
+	regmatches := c.Register.FindStringSubmatch(item)
+	if len(regmatches) == 3 {
+		switch regmatches[1] {
+		case ">":
+			c.PutVar(regmatches[2])
+		case "<":
+			c.GetVar(regmatches[2])
+		}
+
+		return nil
+	}
+
+	// internal commands
+	// FIXME: propagate errors
+	if exists(c.Commands, item) {
+		c.Commands[item].Func(c)
+
+		return nil
+	}
+
+	if exists(c.ShowCommands, item) {
+		c.ShowCommands[item].Func(c)
+
+		return nil
+	}
+
+	if exists(c.StackCommands, item) {
+		c.StackCommands[item].Func(c)
+
+		return nil
+	}
+
+	if exists(c.SettingsCommands, item) {
+		c.SettingsCommands[item].Func(c)
+
+		return nil
+	}
+
+	switch item {
+	case "?":
+		fallthrough
+	case "help":
+		c.PrintHelp()
+
+	default:
+		return Error("unknown command or operator")
+	}
+
+	return nil
 }
 
 // Execute a math function, check if it is defined just in case
@@ -357,10 +383,11 @@ func (c *Calc) DoFuncall(funcname string) error {
 	}
 
 	if function == nil {
-		panic("function not defined but in completion list")
+		return Error("function not defined but in completion list")
 	}
 
 	var args Numbers
+
 	batch := false
 
 	if function.Expectargs == -1 {
@@ -382,11 +409,11 @@ func (c *Calc) DoFuncall(funcname string) error {
 	// 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)
+	funcresult := function.Func(args)
 
-	if R.Err != nil {
+	if funcresult.Err != nil {
 		// leave the stack untouched in case of any error
-		return R.Err
+		return funcresult.Err
 	}
 
 	// don't forget to backup!
@@ -402,10 +429,11 @@ func (c *Calc) DoFuncall(funcname string) error {
 	}
 
 	// save result
-	c.stack.Push(R.Res)
+	c.stack.Push(funcresult.Res)
 
 	// thanks a lot
-	c.SetHistory(funcname, args, R.Res)
+	c.SetHistory(funcname, args, funcresult.Res)
+
 	return nil
 }
 
@@ -430,7 +458,16 @@ func (c *Calc) Result() float64 {
 			fmt.Print("= ")
 		}
 
-		fmt.Println(c.stack.Last()[0])
+		result := c.stack.Last()[0]
+		truncated := math.Trunc(result)
+		precision := c.precision
+
+		if result == truncated {
+			precision = 0
+		}
+
+		format := fmt.Sprintf("%%.%df\n", precision)
+		fmt.Printf(format, result)
 	}
 
 	return c.stack.Last()[0]
@@ -444,24 +481,26 @@ func (c *Calc) Debug(msg string) {
 
 func (c *Calc) EvalLuaFunction(funcname string) {
 	// called from calc loop
-	var x float64
+	var luaresult float64
+
 	var err error
 
 	switch c.interpreter.FuncNumArgs(funcname) {
 	case 0:
 		fallthrough
 	case 1:
-		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last())
+		luaresult, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last())
 	case 2:
-		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last(2))
+		luaresult, err = c.interpreter.CallLuaFunc(funcname, c.stack.Last(2))
 	case -1:
-		x, err = c.interpreter.CallLuaFunc(funcname, c.stack.All())
+		luaresult, err = c.interpreter.CallLuaFunc(funcname, c.stack.All())
 	default:
-		x, err = 0, errors.New("invalid number of argument requested")
+		luaresult, err = 0, errors.New("invalid number of argument requested")
 	}
 
 	if err != nil {
 		fmt.Println(err)
+
 		return
 	}
 
@@ -472,24 +511,26 @@ func (c *Calc) EvalLuaFunction(funcname string) {
 	switch c.interpreter.FuncNumArgs(funcname) {
 	case 0:
 		a := c.stack.Last()
+
 		if len(a) == 1 {
-			c.History("%s(%f) = %f", funcname, a, x)
+			c.History("%s(%f) = %f", funcname, a, luaresult)
 		}
+
 		dopush = false
 	case 1:
 		a := c.stack.Pop()
-		c.History("%s(%f) = %f", funcname, a, x)
+		c.History("%s(%f) = %f", funcname, a, luaresult)
 	case 2:
 		a := c.stack.Pop()
 		b := c.stack.Pop()
-		c.History("%s(%f,%f) = %f", funcname, a, b, x)
+		c.History("%s(%f,%f) = %f", funcname, a, b, luaresult)
 	case -1:
 		c.stack.Clear()
-		c.History("%s(*) = %f", funcname, x)
+		c.History("%s(*) = %f", funcname, luaresult)
 	}
 
 	if dopush {
-		c.stack.Push(x)
+		c.stack.Push(luaresult)
 	}
 
 	c.Result()
@@ -507,7 +548,7 @@ func (c *Calc) PutVar(name string) {
 }
 
 func (c *Calc) GetVar(name string) {
-	if _, ok := c.Vars[name]; ok {
+	if exists(c.Vars, name) {
 		c.Debug(fmt.Sprintf("retrieve %.2f from %s", c.Vars[name], name))
 		c.stack.Backup()
 		c.stack.Push(c.Vars[name])
@@ -520,7 +561,9 @@ func sortcommands(hash Commands) []string {
 	keys := make([]string, 0, len(hash))
 
 	for key := range hash {
-		keys = append(keys, key)
+		if len(key) > 1 {
+			keys = append(keys, key)
+		}
 	}
 
 	sort.Strings(keys)
@@ -530,27 +573,35 @@ func sortcommands(hash Commands) []string {
 
 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)
@@ -558,6 +609,7 @@ func (c *Calc) PrintHelp() {
 	// 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

@@ -19,6 +19,8 @@ package main
 
 import (
 	"fmt"
+	"strconv"
+	"strings"
 	"testing"
 
 	lua "github.com/yuin/gopher-lua"
@@ -69,20 +71,22 @@ func TestCommentsAndWhitespace(t *testing.T) {
 		},
 	}
 
-	for _, tt := range tests {
+	for _, test := range tests {
 		testname := fmt.Sprintf("%s .(expect %.2f)",
-			tt.name, tt.exp)
+			test.name, test.exp)
 
 		t.Run(testname, func(t *testing.T) {
-			for _, line := range tt.cmd {
-				calc.Eval(line)
+			for _, line := range test.cmd {
+				if err := calc.Eval(line); err != nil {
+					t.Errorf(err.Error())
+				}
 			}
 			got := calc.stack.Last()
 
 			if len(got) > 0 {
-				if got[0] != tt.exp {
+				if got[0] != test.exp {
 					t.Errorf("parsing failed:\n+++  got: %f\n--- want: %f",
-						got, tt.exp)
+						got, test.exp)
 				}
 			}
 
@@ -90,7 +94,6 @@ func TestCommentsAndWhitespace(t *testing.T) {
 				t.Errorf("invalid stack size:\n+++  got: %d\n--- want: 1",
 					calc.stack.Len())
 			}
-
 		})
 
 		calc.stack.Clear()
@@ -282,18 +285,20 @@ func TestCalc(t *testing.T) {
 		},
 	}
 
-	for _, tt := range tests {
+	for _, test := range tests {
 		testname := fmt.Sprintf("cmd-%s-expect-%.2f",
-			tt.name, tt.exp)
+			test.name, test.exp)
 
 		t.Run(testname, func(t *testing.T) {
-			calc.batch = tt.batch
-			calc.Eval(tt.cmd)
+			calc.batch = test.batch
+			if err := calc.Eval(test.cmd); err != nil {
+				t.Errorf(err.Error())
+			}
 			got := calc.Result()
 			calc.stack.Clear()
-			if got != tt.exp {
+			if got != test.exp {
 				t.Errorf("calc failed:\n+++  got: %f\n--- want: %f",
-					got, tt.exp)
+					got, test.exp)
 			}
 		})
 	}
@@ -318,23 +323,24 @@ func TestCalcLua(t *testing.T) {
 	}
 
 	calc := NewCalc()
-	L = lua.NewState(lua.Options{SkipOpenLibs: true})
-	defer L.Close()
+
+	LuaInterpreter = lua.NewState(lua.Options{SkipOpenLibs: true})
+	defer LuaInterpreter.Close()
 
 	luarunner := NewInterpreter("example.lua", false)
 	luarunner.InitLua()
 	calc.SetInt(luarunner)
 
-	for _, tt := range tests {
-		testname := fmt.Sprintf("lua-%s", tt.function)
+	for _, test := range tests {
+		testname := fmt.Sprintf("lua-%s", test.function)
 
 		t.Run(testname, func(t *testing.T) {
 			calc.stack.Clear()
-			for _, item := range tt.stack {
+			for _, item := range test.stack {
 				calc.stack.Push(item)
 			}
 
-			calc.EvalLuaFunction(tt.function)
+			calc.EvalLuaFunction(test.function)
 
 			got := calc.stack.Last()
 
@@ -343,10 +349,68 @@ func TestCalcLua(t *testing.T) {
 					calc.stack.Len())
 			}
 
-			if got[0] != tt.exp {
+			if got[0] != test.exp {
 				t.Errorf("lua function %s failed:\n+++  got: %f\n--- want: %f",
-					tt.function, got, tt.exp)
+					test.function, got, test.exp)
 			}
 		})
 	}
 }
+
+func FuzzEval(f *testing.F) {
+	legal := []string{
+		"dump",
+		"showstack",
+		"help",
+		"Pi 31 *",
+		"SqrtE Pi /",
+		"55.5 yards-to-meters",
+		"2 4 +",
+		"7 8 batch sum",
+		"7 8 %-",
+		"7 8 clear",
+		"7 8 /",
+		"b",
+		"#444",
+		"<X",
+	}
+
+	for _, item := range legal {
+		f.Add(item)
+	}
+
+	calc := NewCalc()
+
+	var hexnum int
+
+	f.Fuzz(func(t *testing.T, line string) {
+		t.Logf("Stack:\n%v\n", calc.stack.All())
+		if err := calc.EvalItem(line); err == nil {
+			t.Logf("given: <%s>", line)
+			// not corpus and empty?
+			if !contains(legal, line) && len(line) > 0 {
+				item := strings.TrimSpace(calc.Comment.ReplaceAllString(line, ""))
+				_, hexerr := fmt.Sscanf(item, "0x%x", &hexnum)
+				// no comment?
+				if len(item) > 0 {
+					// no known command or function?
+					if _, err := strconv.ParseFloat(item, 64); err != nil {
+						if !contains(calc.Constants, item) &&
+							!exists(calc.Funcalls, item) &&
+							!exists(calc.BatchFuncalls, item) &&
+							!contains(calc.LuaFunctions, item) &&
+							!exists(calc.Commands, item) &&
+							!exists(calc.ShowCommands, item) &&
+							!exists(calc.SettingsCommands, item) &&
+							!exists(calc.StackCommands, item) &&
+							!calc.Register.MatchString(item) &&
+							item != "?" && item != "help" &&
+							hexerr != nil {
+							t.Errorf("Fuzzy input accepted: <%s>", line)
+						}
+					}
+				}
+			}
+		}
+	})
+}

command.go

@@ -42,9 +42,8 @@ func NewCommand(help string, function CommandFunction) *Command {
 	}
 }
 
-// define all management (that is: non calculation) commands
-func (c *Calc) SetCommands() {
-	c.SettingsCommands = Commands{
+func (c *Calc) SetSettingsCommands() Commands {
+	return Commands{
 		// Toggles
 		"debug": NewCommand(
 			"toggle debugging",
@@ -89,8 +88,10 @@ func (c *Calc) SetCommands() {
 			},
 		),
 	}
+}
 
-	c.ShowCommands = Commands{
+func (c *Calc) SetShowCommands() Commands {
+	return Commands{
 		// Display commands
 		"dump": NewCommand(
 			"display the stack contents",
@@ -131,8 +132,10 @@ func (c *Calc) SetCommands() {
 			},
 		),
 	}
+}
 
-	c.StackCommands = Commands{
+func (c *Calc) SetStackCommands() Commands {
+	return Commands{
 		"clear": NewCommand(
 			"clear the whole stack",
 			func(c *Calc) {
@@ -159,14 +162,7 @@ func (c *Calc) SetCommands() {
 
 		"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()
-				}
-			},
+			CommandSwap,
 		),
 
 		"undo": NewCommand(
@@ -178,113 +174,21 @@ func (c *Calc) SetCommands() {
 
 		"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")
-				}
-			},
+			CommandDup,
 		),
 
 		"edit": NewCommand(
 			"edit the stack interactively",
-			func(c *Calc) {
-				if c.stack.Len() == 0 {
-					fmt.Println("empty stack")
-					return
-				}
-
-				c.stack.Backup()
-
-				// put the stack contents into a tmp file
-				tmp, err := os.CreateTemp("", "stack")
-				if err != nil {
-					fmt.Println(err)
-					return
-				}
-				defer os.Remove(tmp.Name())
-
-				comment := `# add or remove numbers as you wish.
-# each number must be on its own line.
-# numbers must be floating point formatted.
-`
-				_, err = tmp.WriteString(comment)
-				if err != nil {
-					fmt.Println(err)
-					return
-				}
-
-				for _, item := range c.stack.All() {
-					_, err = fmt.Fprintf(tmp, "%f\n", item)
-					if err != nil {
-						fmt.Println(err)
-						return
-					}
-				}
-
-				tmp.Close()
-
-				// determine which editor to use
-				editor := "vi"
-				enveditor, present := os.LookupEnv("EDITOR")
-				if present {
-					if editor != "" {
-						if _, err := os.Stat(editor); err == nil {
-							editor = enveditor
-						}
-					}
-				}
-
-				// execute editor with our tmp file containing current stack
-				cmd := exec.Command(editor, tmp.Name())
-
-				cmd.Stdin = os.Stdin
-				cmd.Stdout = os.Stdout
-				cmd.Stderr = os.Stderr
-
-				err = cmd.Run()
-				if err != nil {
-					fmt.Println("could not run editor command: ", err)
-					return
-				}
-
-				// read the file back in
-				modified, err := os.Open(tmp.Name())
-				if err != nil {
-					fmt.Println("Error opening file:", err)
-					return
-				}
-				defer modified.Close()
-
-				// reset the stack
-				c.stack.Clear()
-
-				// and put the new contents (if legit) back onto the stack
-				scanner := bufio.NewScanner(modified)
-				for scanner.Scan() {
-					line := strings.TrimSpace(c.Comment.ReplaceAllString(scanner.Text(), ""))
-					if line == "" {
-						continue
-					}
-
-					num, err := strconv.ParseFloat(line, 64)
-					if err != nil {
-						fmt.Printf("%s is not a floating point number!\n", line)
-						continue
-					}
-
-					c.stack.Push(num)
-				}
-
-				if err := scanner.Err(); err != nil {
-					fmt.Println("Error reading from file:", err)
-				}
-			},
+			CommandEdit,
 		),
 	}
+}
+
+// define all management (that is: non calculation) commands
+func (c *Calc) SetCommands() {
+	c.SettingsCommands = c.SetSettingsCommands()
+	c.ShowCommands = c.SetShowCommands()
+	c.StackCommands = c.SetStackCommands()
 
 	// general commands
 	c.Commands = Commands{
@@ -317,3 +221,126 @@ func (c *Calc) SetCommands() {
 	c.StackCommands["c"] = c.StackCommands["clear"]
 	c.StackCommands["u"] = c.StackCommands["undo"]
 }
+
+// added to the command map:
+func CommandSwap(c *Calc) {
+	if c.stack.Len() < 2 {
+		fmt.Println("stack too small, can't swap")
+	} else {
+		c.stack.Backup()
+		c.stack.Swap()
+	}
+}
+
+func CommandDup(c *Calc) {
+	item := c.stack.Last()
+	if len(item) == 1 {
+		c.stack.Backup()
+		c.stack.Push(item[0])
+	} else {
+		fmt.Println("stack empty")
+	}
+}
+
+func CommandEdit(calc *Calc) {
+	if calc.stack.Len() == 0 {
+		fmt.Println("empty stack")
+
+		return
+	}
+
+	calc.stack.Backup()
+
+	// put the stack contents into a tmp file
+	tmp, err := os.CreateTemp("", "stack")
+	if err != nil {
+		fmt.Println(err)
+
+		return
+	}
+
+	defer os.Remove(tmp.Name())
+
+	comment := `# add or remove numbers as you wish.
+# each number must be on its own line.
+# numbers must be floating point formatted.
+`
+	_, err = tmp.WriteString(comment)
+
+	if err != nil {
+		fmt.Println(err)
+
+		return
+	}
+
+	for _, item := range calc.stack.All() {
+		_, err = fmt.Fprintf(tmp, "%f\n", item)
+		if err != nil {
+			fmt.Println(err)
+
+			return
+		}
+	}
+
+	tmp.Close()
+
+	// determine which editor to use
+	editor := "vi"
+
+	enveditor, present := os.LookupEnv("EDITOR")
+	if present {
+		if editor != "" {
+			if _, err := os.Stat(editor); err == nil {
+				editor = enveditor
+			}
+		}
+	}
+
+	// execute editor with our tmp file containing current stack
+	cmd := exec.Command(editor, tmp.Name())
+
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	err = cmd.Run()
+	if err != nil {
+		fmt.Println("could not run editor command: ", err)
+
+		return
+	}
+
+	// read the file back in
+	modified, err := os.Open(tmp.Name())
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+
+		return
+	}
+	defer modified.Close()
+
+	// reset the stack
+	calc.stack.Clear()
+
+	// and put the new contents (if legit) back onto the stack
+	scanner := bufio.NewScanner(modified)
+	for scanner.Scan() {
+		line := strings.TrimSpace(calc.Comment.ReplaceAllString(scanner.Text(), ""))
+		if line == "" {
+			continue
+		}
+
+		num, err := strconv.ParseFloat(line, 64)
+		if err != nil {
+			fmt.Printf("%s is not a floating point number!\n", line)
+
+			continue
+		}
+
+		calc.stack.Push(num)
+	}
+
+	if err := scanner.Err(); err != nil {
+		fmt.Println("Error reading from file:", err)
+	}
+}

funcs.go

@@ -22,14 +22,14 @@ import (
 	"math"
 )
 
-type R struct {
+type Result struct {
 	Res float64
 	Err error
 }
 
 type Numbers []float64
 
-type Function func(Numbers) R
+type Function func(Numbers) Result
 
 // 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
@@ -64,438 +64,450 @@ func NewFuncall(function Function, expectargs ...int) *Funcall {
 }
 
 // Convenience function, create new result
-func NewR(n float64, e error) R {
-	return R{Res: n, Err: e}
+func NewResult(n float64, e error) Result {
+	return Result{Res: n, Err: e}
 }
 
 // the actual functions, called once during initialization.
 func DefineFunctions() Funcalls {
-	f := map[string]*Funcall{
+	funcmap := map[string]*Funcall{
 		// simple operators, they all expect 2 args
 		"+": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]+arg[1], nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]+arg[1], nil)
 			},
 		),
 
 		"-": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]-arg[1], nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]-arg[1], nil)
 			},
 		),
 
 		"x": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]*arg[1], nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]*arg[1], nil)
 			},
 		),
 
 		"/": NewFuncall(
-			func(arg Numbers) R {
+			func(arg Numbers) Result {
 				if arg[1] == 0 {
-					return NewR(0, errors.New("division by null"))
+					return NewResult(0, errors.New("division by null"))
 				}
 
-				return NewR(arg[0]/arg[1], nil)
+				return NewResult(arg[0]/arg[1], nil)
 			},
 		),
 
 		"^": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Pow(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Pow(arg[0], arg[1]), nil)
 			},
 		),
 
 		"%": NewFuncall(
-			func(arg Numbers) R {
-				return NewR((arg[0]/100)*arg[1], nil)
+			func(arg Numbers) Result {
+				return NewResult((arg[0]/100)*arg[1], nil)
 			},
 		),
 
 		"%-": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]-((arg[0]/100)*arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]-((arg[0]/100)*arg[1]), nil)
 			},
 		),
 
 		"%+": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]+((arg[0]/100)*arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]+((arg[0]/100)*arg[1]), nil)
 			},
 		),
 
 		"mod": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Remainder(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Remainder(arg[0], arg[1]), nil)
 			},
 		),
 
 		"sqrt": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Sqrt(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Sqrt(arg[0]), nil)
 			},
 			1),
 
 		"abs": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Abs(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Abs(arg[0]), nil)
 			},
 			1),
 
 		"acos": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Acos(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Acos(arg[0]), nil)
 			},
 			1),
 
 		"acosh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Acosh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Acosh(arg[0]), nil)
 			},
 			1),
 
 		"asin": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Asin(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Asin(arg[0]), nil)
 			},
 			1),
 
 		"asinh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Asinh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Asinh(arg[0]), nil)
 			},
 			1),
 
 		"atan": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Atan(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Atan(arg[0]), nil)
 			},
 			1),
 
 		"atan2": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Atan2(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Atan2(arg[0], arg[1]), nil)
 			},
 			2),
 
 		"atanh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Atanh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Atanh(arg[0]), nil)
 			},
 			1),
 
 		"cbrt": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Cbrt(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Cbrt(arg[0]), nil)
 			},
 			1),
 
 		"ceil": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Ceil(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Ceil(arg[0]), nil)
 			},
 			1),
 
 		"cos": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Cos(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Cos(arg[0]), nil)
 			},
 			1),
 
 		"cosh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Cosh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Cosh(arg[0]), nil)
 			},
 			1),
 
 		"erf": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Erf(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Erf(arg[0]), nil)
 			},
 			1),
 
 		"erfc": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Erfc(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Erfc(arg[0]), nil)
 			},
 			1),
 
 		"erfcinv": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Erfcinv(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Erfcinv(arg[0]), nil)
 			},
 			1),
 
 		"erfinv": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Erfinv(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Erfinv(arg[0]), nil)
 			},
 			1),
 
 		"exp": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Exp(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Exp(arg[0]), nil)
 			},
 			1),
 
 		"exp2": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Exp2(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Exp2(arg[0]), nil)
 			},
 			1),
 
 		"expm1": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Expm1(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Expm1(arg[0]), nil)
 			},
 			1),
 
 		"floor": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Floor(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Floor(arg[0]), nil)
 			},
 			1),
 
 		"gamma": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Gamma(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Gamma(arg[0]), nil)
 			},
 			1),
 
 		"ilogb": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(math.Ilogb(arg[0])), nil)
+			func(arg Numbers) Result {
+				return NewResult(float64(math.Ilogb(arg[0])), nil)
 			},
 			1),
 
 		"j0": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.J0(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.J0(arg[0]), nil)
 			},
 			1),
 
 		"j1": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.J1(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.J1(arg[0]), nil)
 			},
 			1),
 
 		"log": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Log(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Log(arg[0]), nil)
 			},
 			1),
 
 		"log10": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Log10(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Log10(arg[0]), nil)
 			},
 			1),
 
 		"log1p": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Log1p(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Log1p(arg[0]), nil)
 			},
 			1),
 
 		"log2": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Log2(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Log2(arg[0]), nil)
 			},
 			1),
 
 		"logb": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Logb(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Logb(arg[0]), nil)
 			},
 			1),
 
 		"pow": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Pow(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Pow(arg[0], arg[1]), nil)
 			},
 			2),
 
 		"round": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Round(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Round(arg[0]), nil)
 			},
 			1),
 
 		"roundtoeven": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.RoundToEven(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.RoundToEven(arg[0]), nil)
 			},
 			1),
 
 		"sin": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Sin(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Sin(arg[0]), nil)
 			},
 			1),
 
 		"sinh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Sinh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Sinh(arg[0]), nil)
 			},
 			1),
 
 		"tan": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Tan(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Tan(arg[0]), nil)
 			},
 			1),
 
 		"tanh": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Tanh(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Tanh(arg[0]), nil)
 			},
 			1),
 
 		"trunc": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Trunc(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Trunc(arg[0]), nil)
 			},
 			1),
 
 		"y0": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Y0(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Y0(arg[0]), nil)
 			},
 			1),
 
 		"y1": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Y1(arg[0]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Y1(arg[0]), nil)
 			},
 			1),
 
 		"copysign": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Copysign(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Copysign(arg[0], arg[1]), nil)
 			},
 			2),
 
 		"dim": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Dim(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Dim(arg[0], arg[1]), nil)
 			},
 			2),
 
 		"hypot": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(math.Hypot(arg[0], arg[1]), nil)
+			func(arg Numbers) Result {
+				return NewResult(math.Hypot(arg[0], arg[1]), nil)
 			},
 			2),
 
 		// converters of all kinds
 		"cm-to-inch": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]/2.54, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]/2.54, nil)
 			},
 			1),
 
 		"inch-to-cm": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]*2.54, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]*2.54, nil)
 			},
 			1),
 
 		"gallons-to-liters": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]*3.785, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]*3.785, nil)
 			},
 			1),
 
 		"liters-to-gallons": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]/3.785, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]/3.785, nil)
 			},
 			1),
 
 		"yards-to-meters": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]*91.44, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]*91.44, nil)
 			},
 			1),
 
 		"meters-to-yards": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]/91.44, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]/91.44, nil)
 			},
 			1),
 
 		"miles-to-kilometers": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]*1.609, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]*1.609, nil)
 			},
 			1),
 
 		"kilometers-to-miles": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(arg[0]/1.609, nil)
+			func(arg Numbers) Result {
+				return NewResult(arg[0]/1.609, nil)
 			},
 			1),
 
 		"or": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(int(arg[0])|int(arg[1])), nil)
+			func(arg Numbers) Result {
+				return NewResult(float64(int(arg[0])|int(arg[1])), nil)
 			},
 			2),
 
 		"and": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(int(arg[0])&int(arg[1])), nil)
+			func(arg Numbers) Result {
+				return NewResult(float64(int(arg[0])&int(arg[1])), nil)
 			},
 			2),
 
 		"xor": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(int(arg[0])^int(arg[1])), nil)
+			func(arg Numbers) Result {
+				return NewResult(float64(int(arg[0])^int(arg[1])), nil)
 			},
 			2),
 
 		"<": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(int(arg[0])<<int(arg[1])), nil)
+			func(arg Numbers) Result {
+				// Shift by negative number provibited, so check it.
+				// Note that we check against uint64 overflow as well here
+				if arg[1] < 0 || uint64(arg[1]) > math.MaxInt64 {
+					return NewResult(0, errors.New("negative shift amount"))
+				}
+
+				return NewResult(float64(int(arg[0])<<int(arg[1])), nil)
 			},
 			2),
 
 		">": NewFuncall(
-			func(arg Numbers) R {
-				return NewR(float64(int(arg[0])>>int(arg[1])), nil)
+			func(arg Numbers) Result {
+				if arg[1] < 0 || uint64(arg[1]) > math.MaxInt64 {
+					return NewResult(0, errors.New("negative shift amount"))
+				}
+
+				return NewResult(float64(int(arg[0])>>int(arg[1])), nil)
 			},
 			2),
 	}
 
 	// aliases
-	f["*"] = f["x"]
-	f["remainder"] = f["mod"]
+	funcmap["*"] = funcmap["x"]
+	funcmap["remainder"] = funcmap["mod"]
 
-	return f
+	return funcmap
 }
 
 func DefineBatchFunctions() Funcalls {
-	f := map[string]*Funcall{
+	funcmap := map[string]*Funcall{
 		"median": NewFuncall(
-			func(args Numbers) R {
+			func(args Numbers) Result {
 				middle := len(args) / 2
-				return NewR(args[middle], nil)
+
+				return NewResult(args[middle], nil)
 			},
 			-1),
 
 		"mean": NewFuncall(
-			func(args Numbers) R {
+			func(args Numbers) Result {
 				var sum float64
 				for _, item := range args {
 					sum += item
 				}
-				return NewR(sum/float64(len(args)), nil)
+
+				return NewResult(sum/float64(len(args)), nil)
 			},
 			-1),
 
 		"min": NewFuncall(
-			func(args Numbers) R {
+			func(args Numbers) Result {
 				var min float64
 				min, args = args[0], args[1:]
 				for _, item := range args {
@@ -503,12 +515,13 @@ func DefineBatchFunctions() Funcalls {
 						min = item
 					}
 				}
-				return NewR(min, nil)
+
+				return NewResult(min, nil)
 			},
 			-1),
 
 		"max": NewFuncall(
-			func(args Numbers) R {
+			func(args Numbers) Result {
 				var max float64
 				max, args = args[0], args[1:]
 				for _, item := range args {
@@ -516,24 +529,26 @@ func DefineBatchFunctions() Funcalls {
 						max = item
 					}
 				}
-				return NewR(max, nil)
+
+				return NewResult(max, nil)
 			},
 			-1),
 
 		"sum": NewFuncall(
-			func(args Numbers) R {
+			func(args Numbers) Result {
 				var sum float64
 				for _, item := range args {
 					sum += item
 				}
-				return NewR(sum, nil)
+
+				return NewResult(sum, nil)
 			},
 			-1),
 	}
 
 	// aliases
-	f["+"] = f["sum"]
-	f["avg"] = f["mean"]
+	funcmap["+"] = funcmap["sum"]
+	funcmap["avg"] = funcmap["mean"]
 
-	return f
+	return funcmap
 }

go.mod

@@ -4,7 +4,9 @@ go 1.20
 
 require (
 	github.com/chzyer/readline v1.5.1 // indirect
+	github.com/rogpeppe/go-internal v1.11.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/yuin/gopher-lua v1.1.0 // indirect
-	golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5 // indirect
+	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f // indirect
+	golang.org/x/tools v0.1.12 // indirect
 )

go.sum

@@ -2,9 +2,15 @@ github.com/chzyer/logex v1.2.1/go.mod h1:JLbx6lG2kDbNRFnfkgvh4eRJRPX1QCoOIWomwys
 github.com/chzyer/readline v1.5.1 h1:upd/6fQk4src78LMRzh5vItIt361/o4uq553V8B5sGI=
 github.com/chzyer/readline v1.5.1/go.mod h1:Eh+b79XXUwfKfcPLepksvw2tcLE/Ct21YObkaSkeBlk=
 github.com/chzyer/test v1.0.0/go.mod h1:2JlltgoNkt4TW/z9V/IzDdFaMTM2JPIi26O1pF38GC8=
+github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
+github.com/rogpeppe/go-internal v1.11.0/go.mod h1:ddIwULY96R17DhadqLgMfk9H9tvdUzkipdSkR5nkCZA=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/yuin/gopher-lua v1.1.0 h1:BojcDhfyDWgU2f2TOzYK/g5p2gxMrku8oupLDqlnSqE=
 github.com/yuin/gopher-lua v1.1.0/go.mod h1:GBR0iDaNXjAgGg9zfCvksxSRnQx76gclCIb7kdAd1Pw=
 golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5 h1:y/woIyUBFbpQGKS0u1aHF/40WUDnek3fPOyD08H5Vng=
 golang.org/x/sys v0.0.0-20220310020820-b874c991c1a5/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
+golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
+golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=

interpreter.go

@@ -29,8 +29,8 @@ type Interpreter struct {
 	script string
 }
 
-// LUA interpreter, instanciated in main()
-var L *lua.LState
+// LuaInterpreter is the lua interpreter, instantiated in main()
+var LuaInterpreter *lua.LState
 
 // holds a user provided lua function
 type LuaFunction struct {
@@ -39,8 +39,8 @@ type LuaFunction struct {
 	numargs int
 }
 
-// must be global since init() is  being called from lua which doesn't
-// have access to the interpreter instance
+// LuaFuncs must be global since init() is being called from lua which
+// doesn't have access to the interpreter instance
 var LuaFuncs map[string]LuaFunction
 
 func NewInterpreter(script string, debug bool) *Interpreter {
@@ -61,8 +61,8 @@ func (i *Interpreter) InitLua() {
 		{lua.DebugLibName, lua.OpenDebug},
 		{lua.MathLibName, lua.OpenMath},
 	} {
-		if err := L.CallByParam(lua.P{
-			Fn:      L.NewFunction(pair.f),
+		if err := LuaInterpreter.CallByParam(lua.P{
+			Fn:      LuaInterpreter.NewFunction(pair.f),
 			NRet:    0,
 			Protect: true,
 		}, lua.LString(pair.n)); err != nil {
@@ -71,19 +71,19 @@ func (i *Interpreter) InitLua() {
 	}
 
 	// load the lua config (which we expect to contain init() and math functions)
-	if err := L.DoFile(i.script); err != nil {
+	if err := LuaInterpreter.DoFile(i.script); err != nil {
 		panic(err)
 	}
 
-	// instanciate
+	// instantiate
 	LuaFuncs = map[string]LuaFunction{}
 
 	// that way the user can call register(...) from lua inside init()
-	L.SetGlobal("register", L.NewFunction(register))
+	LuaInterpreter.SetGlobal("register", LuaInterpreter.NewFunction(register))
 
 	// actually call init()
-	if err := L.CallByParam(lua.P{
-		Fn:      L.GetGlobal("init"),
+	if err := LuaInterpreter.CallByParam(lua.P{
+		Fn:      LuaInterpreter.GetGlobal("init"),
 		NRet:    0,
 		Protect: true,
 	}); err != nil {
@@ -108,9 +108,9 @@ func (i *Interpreter) FuncNumArgs(name string) int {
 // arguments. 1 uses the last item of the stack, 2 the last two and -1
 // all items (which translates to batch mode)
 //
-// The  items  array  will  be   provded  by  calc.Eval(),  these  are
+// The  items  array  will  be  provided  by  calc.Eval(),  these  are
 // non-popped stack  items. So  the items will  only removed  from the
-// stack when the lua function execution is successfull.
+// stack when the lua function execution is successful.
 func (i *Interpreter) CallLuaFunc(funcname string, items []float64) (float64, error) {
 	i.Debug(fmt.Sprintf("calling lua func %s() with %d args",
 		funcname, LuaFuncs[funcname].numargs))
@@ -120,44 +120,44 @@ func (i *Interpreter) CallLuaFunc(funcname string, items []float64) (float64, er
 		fallthrough
 	case 1:
 		// 1 arg variant
-		if err := L.CallByParam(lua.P{
-			Fn:      L.GetGlobal(funcname),
+		if err := LuaInterpreter.CallByParam(lua.P{
+			Fn:      LuaInterpreter.GetGlobal(funcname),
 			NRet:    1,
 			Protect: true,
 		}, lua.LNumber(items[0])); err != nil {
-			fmt.Println(err)
-			return 0, err
+			return 0, fmt.Errorf("failed to exec lua func %s: %w", funcname, err)
 		}
 	case 2:
 		// 2 arg variant
-		if err := L.CallByParam(lua.P{
-			Fn:      L.GetGlobal(funcname),
+		if err := LuaInterpreter.CallByParam(lua.P{
+			Fn:      LuaInterpreter.GetGlobal(funcname),
 			NRet:    1,
 			Protect: true,
 		}, lua.LNumber(items[0]), lua.LNumber(items[1])); err != nil {
-			return 0, err
+			return 0, fmt.Errorf("failed to exec lua func %s: %w", funcname, err)
 		}
 	case -1:
 		// batch variant, use lua table as array
-		tb := L.NewTable()
+		table := LuaInterpreter.NewTable()
 
 		// put the whole stack into it
 		for _, item := range items {
-			tb.Append(lua.LNumber(item))
+			table.Append(lua.LNumber(item))
 		}
 
-		if err := L.CallByParam(lua.P{
-			Fn:      L.GetGlobal(funcname),
+		if err := LuaInterpreter.CallByParam(lua.P{
+			Fn:      LuaInterpreter.GetGlobal(funcname),
 			NRet:    1,
 			Protect: true,
-		}, tb); err != nil {
-			return 0, err
+		}, table); err != nil {
+			return 0, fmt.Errorf("failed to exec lua func %s: %w", funcname, err)
 		}
 	}
 
 	// get result and cast to float64
-	if res, ok := L.Get(-1).(lua.LNumber); ok {
-		L.Pop(1)
+	if res, ok := LuaInterpreter.Get(-1).(lua.LNumber); ok {
+		LuaInterpreter.Pop(1)
+
 		return float64(res), nil
 	}
 
@@ -167,10 +167,10 @@ func (i *Interpreter) CallLuaFunc(funcname string, items []float64) (float64, er
 // called from lua to register a math  function numargs may be 1, 2 or
 // -1, it denotes the number of  items from the stack requested by the
 // lua function. -1 means batch mode, that is all items
-func register(L *lua.LState) int {
-	function := L.ToString(1)
-	numargs := L.ToInt(2)
-	help := L.ToString(3)
+func register(lstate *lua.LState) int {
+	function := lstate.ToString(1)
+	numargs := lstate.ToInt(2)
+	help := lstate.ToString(3)
 
 	LuaFuncs[function] = LuaFunction{
 		name:    function,

main.go

@@ -1,5 +1,5 @@
 /*
-Copyright © 2023 Thomas von Dein
+Copyright © 2023-2024 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
@@ -30,27 +30,33 @@ import (
 	lua "github.com/yuin/gopher-lua"
 )
 
-const VERSION string = "2.0.11"
+const VERSION string = "2.1.0"
 
 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
-  -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
+  -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
+  -c, --config <file>   load <file> containing LUA code
+  -p, --precision <int> floating point number precision (default 2)
+  -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 +
 
-Copyright (c) 2023 T.v.Dein`
+Copyright (c) 2023-2024 T.v.Dein`
 
 func main() {
+	os.Exit(Main())
+}
+
+func Main() int {
 	calc := NewCalc()
 
 	showversion := false
@@ -69,17 +75,20 @@ func main() {
 	flag.BoolVarP(&showmanual, "manual", "m", false, "show manual")
 	flag.StringVarP(&configfile, "config", "c",
 		os.Getenv("HOME")+"/.rpn.lua", "config file (lua format)")
+	flag.IntVarP(&calc.precision, "precision", "p", Precision, "floating point precision")
 
 	flag.Parse()
 
 	if showversion {
 		fmt.Printf("This is rpn version %s\n", VERSION)
-		return
+
+		return 0
 	}
 
 	if showhelp {
 		fmt.Println(Usage)
-		return
+
+		return 0
 	}
 
 	if enabledebug {
@@ -88,12 +97,13 @@ func main() {
 
 	if showmanual {
 		man()
-		os.Exit(0)
+
+		return 0
 	}
 
-	// the lua state object is global, instanciate it early
-	L = lua.NewState(lua.Options{SkipOpenLibs: true})
-	defer L.Close()
+	// the lua state object is global, instantiate it early
+	LuaInterpreter = lua.NewState(lua.Options{SkipOpenLibs: true})
+	defer LuaInterpreter.Close()
 
 	// our config file is interpreted  as lua code, only functions can
 	// be defined, init() will be called by InitLua().
@@ -101,18 +111,29 @@ func main() {
 		luarunner := NewInterpreter(configfile, enabledebug)
 		luarunner.InitLua()
 		calc.SetInt(luarunner)
+
+		if calc.debug {
+			fmt.Println("loaded config")
+		}
+	} else if calc.debug {
+		fmt.Println(err)
 	}
 
 	if len(flag.Args()) > 1 {
 		// commandline calc operation, no readline etc needed
 		// called like rpn 2 2 +
 		calc.stdin = true
-		calc.Eval(strings.Join(flag.Args(), " "))
-		return
+		if err := calc.Eval(strings.Join(flag.Args(), " ")); err != nil {
+			fmt.Println(err)
+
+			return 1
+		}
+
+		return 0
 	}
 
 	// interactive mode, need readline
-	rl, err := readline.NewEx(&readline.Config{
+	reader, err := readline.NewEx(&readline.Config{
 		Prompt:            calc.Prompt(),
 		HistoryFile:       os.Getenv("HOME") + "/.rpn-history",
 		HistoryLimit:      500,
@@ -125,8 +146,8 @@ func main() {
 	if err != nil {
 		panic(err)
 	}
-	defer rl.Close()
-	rl.CaptureExitSignal()
+	defer reader.Close()
+	reader.CaptureExitSignal()
 
 	if inputIsStdin() {
 		// commands are  coming on stdin, however we  will still enter
@@ -136,13 +157,17 @@ func main() {
 
 	for {
 		// primary program repl
-		line, err := rl.Readline()
+		line, err := reader.Readline()
 		if err != nil {
 			break
 		}
 
-		calc.Eval(line)
-		rl.SetPrompt(calc.Prompt())
+		err = calc.Eval(line)
+		if err != nil {
+			fmt.Println(err)
+		}
+
+		reader.SetPrompt(calc.Prompt())
 	}
 
 	if len(flag.Args()) > 0 {
@@ -150,23 +175,31 @@ func main() {
 		// echo 1 2 3 4 | rpn +
 		// batch mode enabled automatically
 		calc.batch = true
-		calc.Eval(flag.Args()[0])
+		if err = calc.Eval(flag.Args()[0]); err != nil {
+			fmt.Println(err)
+
+			return 1
+		}
 	}
+
+	return 0
 }
 
 func inputIsStdin() bool {
 	stat, _ := os.Stdin.Stat()
+
 	return (stat.Mode() & os.ModeCharDevice) == 0
 }
 
 func man() {
+	var buf bytes.Buffer
+
 	man := exec.Command("less", "-")
 
-	var b bytes.Buffer
-	b.Write([]byte(manpage))
+	buf.WriteString(manpage)
 
 	man.Stdout = os.Stdout
-	man.Stdin = &b
+	man.Stdin = &buf
 	man.Stderr = os.Stderr
 
 	err := man.Run()

main_test.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"os"
+	"testing"
+
+	"github.com/rogpeppe/go-internal/testscript"
+)
+
+func TestMain(m *testing.M) {
+	os.Exit(testscript.RunMain(m, map[string]func() int{
+		"testrpn": Main,
+	}))
+}
+
+func TestRpn(t *testing.T) {
+	testscript.Run(t, testscript.Params{
+		Dir: "t",
+	})
+}

rpn.go

@@ -8,13 +8,15 @@ SYNOPSIS
         Usage: rpn [-bdvh] [<operator>]
     
         Options:
-          -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
+          -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
+          -c, --config <file>   load <file> containing LUA code
+          -p, --precision <int> floating point number precision (default 2)
+          -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 +
@@ -127,7 +129,7 @@ DESCRIPTION
     Basic operators:
 
         +                    add
-        -                    substract
+        -                    subtract
         /                    divide
         x                    multiply (alias: *)
         ^                    power
@@ -143,7 +145,7 @@ DESCRIPTION
     Percent functions:
 
         %                    percent
-        %-                   substract percent
+        %-                   subtract percent
         %+                   add percent
 
     Batch functions:
@@ -309,6 +311,15 @@ EXTENDING RPN USING LUA
     So you can't open files, execute other programs or open a connection to
     the outside!
 
+CONFIGURATION
+    rpn can be configured via command line flags (see usage above). Most of
+    the flags are also available as interactive commands, such as "--batch"
+    has the same effect as the batch command.
+
+    The floating point number precision option "-p, --precision" however is
+    not available as interactive command, it MUST be configured on the
+    command line, if needed. The default precision is 2.
+
 GETTING HELP
     In interactive mode you can enter the help command (or ?) to get a short
     help along with a list of all supported operators and functions.
@@ -328,7 +339,7 @@ LICENSE
     This software is licensed under the GNU GENERAL PUBLIC LICENSE version
     3.
 
-    Copyright (c) 2023 by Thomas von Dein
+    Copyright (c) 2023-2024 by Thomas von Dein
 
     This software uses the following GO modules:
 

rpn.pod

@@ -7,13 +7,15 @@ rpn - Programmable command-line calculator using reverse polish notation
     Usage: rpn [-bdvh] [<operator>]
     
     Options:
-      -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
+      -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
+      -c, --config <file>   load <file> containing LUA code
+      -p, --precision <int> floating point number precision (default 2)
+      -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 +
@@ -134,7 +136,7 @@ stack.
 Basic operators:
 
     +                    add
-    -                    substract
+    -                    subtract
     /                    divide
     x                    multiply (alias: *)
     ^                    power
@@ -150,7 +152,7 @@ Bitwise operators:
 Percent functions:
 
     %                    percent
-    %-                   substract percent
+    %-                   subtract percent
     %+                   add percent
 
 Batch functions:
@@ -342,6 +344,16 @@ B<Please note, that io, networking and system stuff is not allowed
 though. So you can't open files, execute other programs or open a
 connection to the outside!>
 
+=head1 CONFIGURATION
+
+B<rpn> can be configured via command line flags (see usage
+above). Most of the flags are also available as interactive commands,
+such as C<--batch> has the same effect as the B<batch> command.
+
+The floating point number  precision option C<-p, --precision> however
+is not available as interactive command,  it MUST be configured on the
+command line, if needed. The default precision is 2.
+
 =head1 GETTING HELP
 
 In interactive mode you can enter the B<help> command (or B<?>) to get
@@ -364,7 +376,7 @@ L<https://github.com/TLINDEN/rpnc/issues>.
 
 This software is licensed under the GNU GENERAL PUBLIC LICENSE version 3.
 
-Copyright (c) 2023 by Thomas von Dein
+Copyright (c) 2023-2024 by Thomas von Dein
 
 This software uses the following GO modules:
 

stack.go

@@ -64,14 +64,14 @@ func (s *Stack) Bump() {
 }
 
 // append an item to the stack
-func (s *Stack) Push(x float64) {
+func (s *Stack) Push(item float64) {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
-	s.Debug(fmt.Sprintf("     push to stack: %.2f", x))
+	s.Debug(fmt.Sprintf("     push to stack: %.2f", item))
 
 	s.Bump()
-	s.linklist.PushBack(x)
+	s.linklist.PushBack(item)
 }
 
 // remove and return an item from the stack
@@ -90,6 +90,7 @@ func (s *Stack) Pop() float64 {
 	s.Debug(fmt.Sprintf(" remove from stack: %.2f", val))
 
 	s.Bump()
+
 	return val.(float64)
 }
 
@@ -123,32 +124,33 @@ func (s *Stack) Swap() {
 		return
 	}
 
-	a := s.linklist.Back()
-	s.linklist.Remove(a)
+	prevA := s.linklist.Back()
+	s.linklist.Remove(prevA)
 
-	b := s.linklist.Back()
-	s.linklist.Remove(b)
+	prevB := s.linklist.Back()
+	s.linklist.Remove(prevB)
 
-	s.Debug(fmt.Sprintf("swapping %.2f with %.2f", b.Value, a.Value))
+	s.Debug(fmt.Sprintf("swapping %.2f with %.2f", prevB.Value, prevA.Value))
 
-	s.linklist.PushBack(a.Value)
-	s.linklist.PushBack(b.Value)
+	s.linklist.PushBack(prevA.Value)
+	s.linklist.PushBack(prevB.Value)
 }
 
 // Return the last num items from the stack w/o modifying it.
 func (s *Stack) Last(num ...int) []float64 {
 	items := []float64{}
-	i := s.Len()
+	stacklen := s.Len()
 	count := 1
+
 	if len(num) > 0 {
 		count = num[0]
 	}
 
 	for e := s.linklist.Front(); e != nil; e = e.Next() {
-		if i <= count {
+		if stacklen <= count {
 			items = append(items, e.Value.(float64))
 		}
-		i--
+		stacklen--
 	}
 
 	return items
@@ -168,12 +170,14 @@ func (s *Stack) All() []float64 {
 // dump the stack to stdout, including backup if debug is enabled
 func (s *Stack) Dump() {
 	fmt.Printf("Stack revision %d (%p):\n", s.rev, &s.linklist)
+
 	for e := s.linklist.Front(); e != nil; e = e.Next() {
 		fmt.Println(e.Value)
 	}
 
 	if s.debug {
 		fmt.Printf("Backup stack revision %d (%p):\n", s.backuprev, &s.backup)
+
 		for e := s.backup.Front(); e != nil; e = e.Next() {
 			fmt.Println(e.Value)
 		}
@@ -215,6 +219,7 @@ func (s *Stack) Restore() {
 
 	if s.rev == 0 {
 		fmt.Println("error: stack is empty.")
+
 		return
 	}
 

stack_test.go

@@ -35,16 +35,16 @@ func TestPush(t *testing.T) {
 
 func TestPop(t *testing.T) {
 	t.Run("pop", func(t *testing.T) {
-		s := NewStack()
-		s.Push(5)
-		got := s.Pop()
+		stack := NewStack()
+		stack.Push(5)
+		got := stack.Pop()
 
 		if got != 5.0 {
 			t.Errorf("pop failed:\n+++  got: %f\n--- want: %f",
 				got, 5.0)
 		}
 
-		if s.Len() != 0 {
+		if stack.Len() != 0 {
 			t.Errorf("stack not empty after pop()")
 		}
 	})
@@ -52,25 +52,25 @@ func TestPop(t *testing.T) {
 
 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()
+		stack := NewStack()
+		stack.Push(5)
+		stack.Push(5)
+		stack.Push(5)
+		stack.Pop()
 
-		if s.Len() != 2 {
+		if stack.Len() != 2 {
 			t.Errorf("stack len not correct after pop:\n+++  got: %d\n--- want: %d",
-				s.Len(), 2)
+				stack.Len(), 2)
 		}
 	})
 }
 
 func TestShift(t *testing.T) {
 	t.Run("shift", func(t *testing.T) {
-		s := NewStack()
-		s.Shift()
+		stack := NewStack()
+		stack.Shift()
 
-		if s.Len() != 0 {
+		if stack.Len() != 0 {
 			t.Errorf("stack not empty after shift()")
 		}
 	})
@@ -78,13 +78,13 @@ func TestShift(t *testing.T) {
 
 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()
+		stack := NewStack()
+		stack.Push(5)
+		stack.Push(5)
+		stack.Push(5)
+		stack.Clear()
 
-		if s.Len() != 0 {
+		if stack.Len() != 0 {
 			t.Errorf("stack not empty after clear()")
 		}
 	})
@@ -92,9 +92,9 @@ func TestClear(t *testing.T) {
 
 func TestLast(t *testing.T) {
 	t.Run("last", func(t *testing.T) {
-		s := NewStack()
-		s.Push(5)
-		got := s.Last()
+		stack := NewStack()
+		stack.Push(5)
+		got := stack.Last()
 
 		if len(got) != 1 {
 			t.Errorf("last failed:\n+++  got: %d elements\n--- want: %d elements",
@@ -106,7 +106,7 @@ func TestLast(t *testing.T) {
 				got, 5.0)
 		}
 
-		if s.Len() != 1 {
+		if stack.Len() != 1 {
 			t.Errorf("stack modified after last()")
 		}
 	})
@@ -114,14 +114,14 @@ func TestLast(t *testing.T) {
 
 func TestAll(t *testing.T) {
 	t.Run("all", func(t *testing.T) {
-		s := NewStack()
+		stack := NewStack()
 		list := []float64{2, 4, 6, 8}
 
 		for _, item := range list {
-			s.Push(item)
+			stack.Push(item)
 		}
 
-		got := s.All()
+		got := stack.All()
 
 		if len(got) != len(list) {
 			t.Errorf("all failed:\n+++  got: %d elements\n--- want: %d elements",
@@ -135,7 +135,7 @@ func TestAll(t *testing.T) {
 			}
 		}
 
-		if s.Len() != len(list) {
+		if stack.Len() != len(list) {
 			t.Errorf("stack modified after last()")
 		}
 	})
@@ -143,37 +143,37 @@ func TestAll(t *testing.T) {
 
 func TestBackupRestore(t *testing.T) {
 	t.Run("shift", func(t *testing.T) {
-		s := NewStack()
-		s.Push(5)
-		s.Backup()
-		s.Clear()
-		s.Restore()
+		stack := NewStack()
+		stack.Push(5)
+		stack.Backup()
+		stack.Clear()
+		stack.Restore()
 
-		if s.Len() != 1 {
+		if stack.Len() != 1 {
 			t.Errorf("stack not correctly restored()")
 		}
 
-		a := s.Pop()
-		if a != 5.0 {
+		value := stack.Pop()
+		if value != 5.0 {
 			t.Errorf("stack not identical to old revision:\n+++  got: %f\n--- want: %f",
-				a, 5.0)
+				value, 5.0)
 		}
 	})
 }
 
 func TestReverse(t *testing.T) {
 	t.Run("reverse", func(t *testing.T) {
-		s := NewStack()
+		stack := NewStack()
 		list := []float64{2, 4, 6}
 		reverse := []float64{6, 4, 2}
 
 		for _, item := range list {
-			s.Push(item)
+			stack.Push(item)
 		}
 
-		s.Reverse()
+		stack.Reverse()
 
-		got := s.All()
+		got := stack.All()
 
 		if len(got) != len(list) {
 			t.Errorf("all failed:\n+++  got: %d elements\n--- want: %d elements",

t/cmdline-command.txtar

@@ -0,0 +1,2 @@
+exec testrpn 1 2 dump
+stdout 'Stack revision 2 .0x'

t/cmdline-invalidcommand.txtar

@@ -0,0 +1,2 @@
+! exec testrpn 1 2 dumb
+stdout 'unknown command or operator'

t/cmdline-precision.txtar

@@ -0,0 +1,2 @@
+exec testrpn -p 4 2 3 /
+stdout '0.6667\n'

t/cmdline-short-stack.txtar

@@ -0,0 +1,2 @@
+! exec testrpn 4 +
+stdout 'stack doesn''t provide enough arguments'

t/cmdlinecalc-debug.txtar

@@ -0,0 +1,2 @@
+exec testrpn -d 44 55 *
+stdout 'push to stack: 2420.00\n'

t/cmdlinecalc-divzero.txtar

@@ -0,0 +1,2 @@
+! exec testrpn 100 50 50 - /
+stdout 'division by null'

t/cmdlinecalc-lua.txtar

@@ -0,0 +1,16 @@
+exec testrpn -d -c test.lua 3 5 lower
+stdout '3\n'
+
+-- test.lua --
+function lower(a,b)
+    if a < b then
+        return a
+    else
+        return b
+    end
+end
+
+function init()
+    -- expects 2 args
+    register("lower", 2, "lower")
+end

t/cmdlinecalc.txtar

@@ -0,0 +1,2 @@
+exec testrpn 44 55 *
+stdout '2420\n'

t/getman.txtar

@@ -0,0 +1,2 @@
+exec testrpn -m
+stdout 'This software is licensed under the GNU GENERAL PUBLIC LICENSE'

t/getusage.txtar

@@ -0,0 +1,2 @@
+exec testrpn -h
+stdout 'This is rpn'

t/getversion.txtar

@@ -0,0 +1,2 @@
+exec testrpn -v
+stdout 'This is rpn version'

t/stdin-batch-cmd.txtar

@@ -0,0 +1,4 @@
+exec echo 1 2 3 4 5 batch median
+stdin stdout
+exec testrpn
+[unix] stdout '3\n'

t/stdin-batch.txtar

@@ -0,0 +1,4 @@
+exec echo 1 2 3 4 5
+stdin stdout
+[unix] exec testrpn median
+[unix] stdout '3\n'

t/stdin-calc.txtar

@@ -0,0 +1,4 @@
+exec echo 10 10 +
+stdin stdout
+exec testrpn
+[unix] stdout '20\n'

t/stdin-help.txtar

@@ -0,0 +1,6 @@
+stdin input.txt
+exec testrpn
+[unix] stdout 'Available configuration commands'
+
+-- input.txt --
+?

t/stdin-use-vars.txtar

@@ -0,0 +1,13 @@
+stdin input.txt
+exec testrpn
+[unix] stdout '28\n'
+
+-- input.txt --
+10
+10
++
+>SUM
+clear
+8
+<SUM
++

t/stdint-explicit-batch.txtar

@@ -0,0 +1,4 @@
+exec echo 1 2 3 4 5 median
+stdin stdout
+exec testrpn -b
+[unix] stdout '3\n'

t/test.lua

@@ -0,0 +1,13 @@
+-- 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
+
+function init()
+    -- expects 2 args
+    register("lower", 2, "lower")
+end  

util.go

@@ -23,13 +23,23 @@ import (
 	"strings"
 )
 
-// find an item in a list
-func contains(s []string, e string) bool {
-	for _, a := range s {
-		if a == e {
+// find an item in a list, generic variant
+func contains[E comparable](s []E, v E) bool {
+	for _, vs := range s {
+		if v == vs {
 			return true
 		}
 	}
+
+	return false
+}
+
+// look if a key in a map exists, generic variant
+func exists[K comparable, V any](m map[K]V, v K) bool {
+	if _, ok := m[v]; ok {
+		return true
+	}
+
 	return false
 }
 
@@ -63,3 +73,7 @@ func const2num(name string) float64 {
 func list2str(list Numbers) string {
 	return strings.Trim(strings.Join(strings.Fields(fmt.Sprint(list)), " "), "[]")
 }
+
+func Error(m string) error {
+	return fmt.Errorf("Error: %s", m)
+}