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path: root/repl/repl.go
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package repl

import (
	"bufio"
	_ "embed"
	"fmt"
	"io"

	"monkey/evaluator"
	"monkey/lexer"
	"monkey/object"
	"monkey/parser"
)

const prompt = ">> "

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

	for {
		fmt.Print(prompt)
		if !scanner.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
		}

		evaluator.DefineMacros(program, macroEnv)
		expanded := evaluator.ExpandMacros(program, macroEnv)

		evaluated := evaluator.Eval(expanded, env)
		if evaluated != nil {
			io.WriteString(out, evaluated.Inspect())
			io.WriteString(out, "\n")
		}
	}
}

//go:embed face.txt
var monkeyFace string

func printParserErrors(out io.Writer, errors []error) {
	fmt.Fprintln(out, monkeyFace)
	for _, err := range errors {
		fmt.Fprintln(out, err)
	}
}