Add REPL boilerplate.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

cmd/repl/main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/repl"
+)
+
+func main() {
+	user, err := user.Current()
+	if err != nil {
+		panic(err)
+	}
+	fmt.Printf("Hello %s, this is the Monkey programming language!\n", user.Username)
+	fmt.Println("Go ahead, type something :)")
+	repl.Start(os.Stdin, os.Stdout)
+}

pkg/repl/repl.go

@@ -0,0 +1,26 @@
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+
+	"code.jmug.me/jmug/interpreter-in-go/pkg/lexer"
+	"code.jmug.me/jmug/interpreter-in-go/pkg/token"
+)
+
+const PROMPT = ">> "
+
+func Start(in io.Reader, out io.Writer) {
+	scanner := bufio.NewScanner(in)
+	for {
+		fmt.Fprint(out, PROMPT)
+		if !scanner.Scan() {
+			return
+		}
+		l := lexer.New(scanner.Text())
+		for tok := l.NextToken(); tok.Type != token.EOF; tok = l.NextToken() {
+			fmt.Fprintf(out, "%+v\n", tok)
+		}
+	}
+}