From 31a0ddd547f2ef6e3288080db458baf28deb40bb Mon Sep 17 00:00:00 2001
From: "T.v.Dein" <git@daemon.de>
Date: Wed, 8 Nov 2023 14:47:15 +0100
Subject: [PATCH] add variable support, implements #10 (#14)

---
 README.md |  1 +
 calc.go   | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++-----
 rpn.go    | 14 ++++++++++++
 rpn.pod   | 14 ++++++++++++
 4 files changed, 88 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index db8c4e7..0904e76 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,7 @@ Features:
 - completion
 - history
 - comments (comment character is `#`)
+- variables
 
 ## Demo
 
diff --git a/calc.go b/calc.go
index 77dc9ff..dedc461 100644
--- a/calc.go
+++ b/calc.go
@@ -41,11 +41,14 @@ type Calc struct {
 	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
@@ -58,6 +61,7 @@ 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
@@ -81,12 +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 swap show`
+	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`
 )
 
@@ -128,6 +136,7 @@ func NewCalc() *Calc {
 
 	c.Funcalls = DefineFunctions()
 	c.BatchFuncalls = DefineBatchFunctions()
+	c.Vars = map[string]float64{}
 
 	c.completer = readline.NewPrefixCompleter(
 		// custom lua functions
@@ -137,6 +146,7 @@ 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, " ")
@@ -253,15 +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()
@@ -301,6 +324,16 @@ func (c *Calc) Eval(line string) {
 				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!")
 			}
@@ -449,3 +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")
+	}
+}
diff --git a/rpn.go b/rpn.go
index ef4b85f..4b6bee6 100644
--- a/rpn.go
+++ b/rpn.go
@@ -164,6 +164,11 @@ DESCRIPTION
         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
@@ -205,6 +210,15 @@ COMMENTS
 
     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
diff --git a/rpn.pod b/rpn.pod
index 43f8a0e..7fce755 100644
--- a/rpn.pod
+++ b/rpn.pod
@@ -172,6 +172,11 @@ Commands:
     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
@@ -226,6 +231,15 @@ append comments to rpn input, e.g.:
 
 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