feat: adds repl to interpreter

main.go

@@ -0,0 +1,19 @@
+package main
+
+import (
+	"Go-interpreter/repl"
+	"fmt"
+	"os"
+	"os/user"
+)
+
+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.Printf("Feel free to type in commands\n")
+	repl.Start(os.Stdin, os.Stdout)
+}

repl/repl.go

@@ -0,0 +1,58 @@
+package repl
+
+import (
+	"Go-interpreter/lexer"
+	"Go-interpreter/parser"
+	"bufio"
+	"fmt"
+	"io"
+)
+
+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)
+		p := parser.New(l)
+
+		program := p.ParseProgram()
+		if len(p.Errors()) != 0 {
+			printParserErrors(out, p.Errors())
+			continue
+		}
+
+		io.WriteString(out, program.String())
+		io.WriteString(out, "\n")
+	}
+}
+
+const MONKEY_FACE = `            __,__
+   .--.  .-"     "-.  .--.
+  / .. \/  .-. .-.  \/ .. \
+ | |  '|  /   Y   \  |'  | |
+ | \   \  \ 0 | 0 /  /   / |
+  \ '- ,\.-"""""""-./, -' /
+   ''-' /_   ^ ^   _\ '-''
+       |  \._   _./  |
+       \   \ '~' /   /
+        '._ '-=-' _.'
+           '-----'
+`
+
+func printParserErrors(out io.Writer, errors []string) {
+	io.WriteString(out, MONKEY_FACE)
+	io.WriteString(out, "Woops! We ran into some monkey business here!\n")
+	io.WriteString(out, " parser errors:\n")
+	for _, msg := range errors {
+		io.WriteString(out, "\t"+msg+"\n")
+	}
+}