1.5 REPL (basic)

cedrickchee · cedrickchee · commit 02a5f71699fd · 2020-03-26T18:15:21.000+08:00
diff --git a/main.go b/main.go
@@ -0,0 +1,22 @@
+package main
+
+// Package main implements the main process which invokes the interpreter's
+// REPL and waits for user input before lexing, parsing nad evaulating.
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+
+	"github.com/cedrickchee/hou/repl"
+)
+
+func main() {
+	user, err := user.Current()
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("Hello %s! This is the Hou programming language!\n", user.Username)
+	fmt.Printf("Feel free to type in commands\n")
+	repl.Start(os.Stdin, os.Stdout)
+}
diff --git a/repl/repl.go b/repl/repl.go
@@ -0,0 +1,37 @@
+package repl
+
+// Package repl implements the Read-Eval-Print-Loop (REPL) or interactive console
+// by lexing, parsing and evaluating the input in the interpreter.
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+
+	"github.com/cedrickchee/hou/lexer"
+	"github.com/cedrickchee/hou/token"
+)
+
+// PROMPT is the REPL prompt displayed for each input.
+const PROMPT = ">> "
+
+// Start starts the REPL in a continuous loop.
+func Start(in io.Reader, out io.Writer) {
+	scanner := bufio.NewScanner(in)
+
+	for {
+		fmt.Printf(PROMPT)
+		scanned := scanner.Scan()
+		if !scanned {
+			return
+		}
+
+		line := scanner.Text()
+
+		// A REPL that tokenizes Monkey source code and prints the tokens.
+		l := lexer.New(line)
+		for tok := l.NextToken(); tok.Type != token.EOF; tok = l.NextToken() {
+			fmt.Printf("%+v\n", tok)
+		}
+	}
+}
