feat: read from std in

Makefile

@@ -5,4 +5,4 @@ it:
 	@ chmod +x ${BINARY_NAME}
 
 ex: it
-	@ ./lambda.exe -v "(\add.(add (add \f.\x.x)) \n.\f.\x.(f ((n f) x)))"
+	@ ./lambda.exe - < ./samples/simple.txt

cmd/lambda/lambda.go

@@ -20,6 +20,11 @@ func main() {
 	logger.Info("Using program arguments.", "args", os.Args)
 	logger.Info("Parsed CLI options.", "options", options)
 
+	if options.Input == "-" {
+		options.Input, err = cli.ReadInput()
+		cli.HandleError(err)
+	}
+
 	tokens, fails := tokenizer.GetTokens([]rune(options.Input))
 	if len(fails) > 0 {
 		cli.HandleError(errors.Join(fails...))

internal/cli/read.go

@@ -0,0 +1,15 @@
+package cli
+
+import (
+	"io"
+	"os"
+)
+
+func ReadInput() (string, error) {
+	data, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		return "", err
+	}
+
+	return string(data), nil
+}

samples/simple.txt

@@ -0,0 +1 @@
+(\add.(add (add (add \f.\x.x))) \n.\f.\x.(f ((n f) x)))