Monkey/repl/repl.go

package repl

import (
	"bufio"
	"fmt"
	"github/runnignwater/monkey/evaluator"
	"github/runnignwater/monkey/lexer"
	"github/runnignwater/monkey/object"
	"github/runnignwater/monkey/parser"
	"io"
	"log"
)

/**
 * @Author: simon
 * @Author: ynwdlxm@163.com
 * @Date: 2022/10/2 下午5:41
 * @Desc: REPL that tokenizes Monkey source code and prints the tokens
 */

const PROMPT = ">>> "

func Start(in io.Reader, out io.Writer) {
	scanner := bufio.NewScanner(in)
	env := object.NewEnvironment()

	for {
		fmt.Printf(PROMPT)
		scan := scanner.Scan()
		if !scan {
			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
		}

		evaluated := evaluator.Eval(program, env)
		if evaluated != nil {
			if _, err := io.WriteString(out, evaluated.Inspect()); err != nil {
				panic(err)
			}
			if _, err := io.WriteString(out, "\n"); err != nil {
				panic(err)
			}
		}
	}
}

func printParserErrors(out io.Writer, errors []string) {
	if _, err := io.WriteString(out, "Woops! we ran into some monkey business here!\n"); err != nil {
		log.Fatal(err)
	}
	if _, err := io.WriteString(out, " parser errors:\n"); err != nil {
		log.Fatal(err)
	}
	for _, msg := range errors {
		_, err := io.WriteString(out, "\t"+msg+"\n")
		if err != nil {
			return
		}
	}
}