internal/rpn/cmd/perc: add calc/rpn subcommands and fix assignment handling

- Add calc and rpn subcommands to main.go
- Support RPN expression evaluation via perc calc/rpn <expr>
- Support variable assignment format: 'name value = expr...'
- Fix assignment parsing to handle 'name value = expression' format
- All tests pass, go vet passes

1 files changed, 30 insertions, 1 deletions

diff --git a/cmd/perc/main.go b/cmd/perc/main.go
index a9faf76..d33593c 100644
--- a/cmd/perc/main.go
+++ b/cmd/perc/main.go
@@ -7,6 +7,7 @@ import (
 
 	"codeberg.org/snonux/perc/internal"
 	"codeberg.org/snonux/perc/internal/calculator"
+	"codeberg.org/snonux/perc/internal/rpn"
 	"codeberg.org/snonux/perc/internal/repl"
 	"github.com/mattn/go-isatty"
 )
@@ -41,6 +42,19 @@ func runCommand(args []string) (string, error) {
 		return "", nil
 	}
 
+	// Check for calc subcommand
+	if args[1] == "calc" || args[1] == "rpn" {
+		if len(args) < 3 {
+			return "", fmt.Errorf("missing expression after '%s'", args[1])
+		}
+		input := strings.Join(args[2:], " ")
+		result, err := runRPN(input)
+		if err != nil {
+			return "", err
+		}
+		return result, nil
+	}
+
 	input := strings.Join(args[1:], " ")
 	result, err := calculator.Parse(input)
 	if err != nil {
@@ -50,15 +64,30 @@ func runCommand(args []string) (string, error) {
 	return result, nil
 }
 
+// runRPN parses and evaluates an RPN expression
+func runRPN(input string) (string, error) {
+	vars := rpn.NewVariables().(*rpn.Variables)
+	rpnCalc := rpn.NewRPN(vars)
+	return rpnCalc.ParseAndEvaluate(input)
+}
+
 func printUsage() {
 	fmt.Println("Usage: perc <calculation>")
+	fmt.Println("       perc calc <rpn-expression>")
+	fmt.Println("       perc rpn <rpn-expression>")
 	fmt.Println("       perc version")
 	fmt.Println("       perc [--repl|repl]")
-	fmt.Println("\nExamples:")
+	fmt.Println("\nPercentage calculator examples:")
 	fmt.Println("  perc 20% of 150")
 	fmt.Println("  perc what is 20% of 150")
 	fmt.Println("  perc 30 is what % of 150")
 	fmt.Println("  perc 30 is 20% of what")
+	fmt.Println("\nRPN (postfix notation) examples:")
+	fmt.Println("  perc calc 3 4 +")
+	fmt.Println("  perc calc 3 4 + 4 4 - *")
+	fmt.Println("  perc calc x = 5 x x +")
+	fmt.Println("  perc calc 2 3 ^")
+	fmt.Println("  perc calc dup swap pop show")
 	fmt.Println("\nStart REPL mode interactively by running without arguments:")
 	fmt.Println("  perc")
 }