repl: support a simple REPL for some early testing

The REPL reads the input, send it to the lexer, and prints the token to
STDOUT. For now nothing else is done since we still don't parse the
tokens.

2 files changed, 41 insertions, 0 deletions

diff --git a/users/fcuny/exp/monkey/cmd/repl/main.go b/users/fcuny/exp/monkey/cmd/repl/main.go
new file mode 100644
index 0000000..46b865c
--- /dev/null
+++ b/users/fcuny/exp/monkey/cmd/repl/main.go
@@ -0,0 +1,12 @@
+package main
+
+import (
+	"fmt"
+	"monkey/pkg/repl"
+	"os"
+)
+
+func main() {
+	fmt.Printf("Welcome to monkey's REPL.")
+	repl.Start(os.Stdin, os.Stdout)
+}
diff --git a/users/fcuny/exp/monkey/pkg/repl/repl.go b/users/fcuny/exp/monkey/pkg/repl/repl.go
new file mode 100644
index 0000000..e8b3b1f
--- /dev/null
+++ b/users/fcuny/exp/monkey/pkg/repl/repl.go
@@ -0,0 +1,29 @@
+package repl
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	lexer "monkey/pkg/lexer"
+	token "monkey/pkg/token"
+)
+
+const PROMPT = ">> "
+
+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()
+		l := lexer.New(line)
+		for tok := l.NextToken(); tok.Type != token.EOF; tok = l.NextToken() {
+			fmt.Printf("%+v\n", tok)
+		}
+	}
+}