transpiler.go

package main

import (
	"flag"
	"fmt"
	"io/ioutil"
	"strconv"
)

type RuneIter struct {
	runes []rune
	cur   int
	size  int
}

type IterError struct {
	error string
}

func (e *IterError) Error() string {
	return fmt.Sprintf("%s\n", e.error)
}

func NewRuneIter(s string) RuneIter {
	runes := make([]rune, 0)
	for _, r := range s {
		runes = append(runes, r)
	}
	return RuneIter{runes, 0, len(runes)}
}

func (r *RuneIter) Peek() (rune, error) {
	if r.cur+1 > r.size-1 {
		return 'a', &IterError{"No more elements"}
	}
	return r.runes[r.cur], nil
}

func (r *RuneIter) Next() (rune, error) {
	if r.cur+1 > r.size-1 {
		return 'a', &IterError{"No more elements"}
	}
	n := r.runes[r.cur]
	r.cur += 1
	return n, nil
}

var cFile = flag.String("c", "", "output file")

var cHead = `
#include <stdio.h>

int
main() {
  char array[1000];
  char *ptr = array;

`

var cTail = `
  return 0;
}
`

var indent = `  `

func addIndent(indentLevel int, s string) string {
	var indented string
	for i := 0; i < indentLevel; i++ {
		indented += indent
	}
	indented += s
	return indented
}

func makeCSource(bfSource string) string {
	cSource := cHead
	indentLevel := 1

	rIter := NewRuneIter(bfSource)

	for {
		indentChange := 0
		rune, err := rIter.Next()
		if err != nil {
			break
		}
		var addC string
		switch rune {
		case '>':
			num := 1
			for {
				peeked, err := rIter.Peek()
				if err != nil {
					break // End of the bf.
				}
				if peeked == '>' {
					num += 1
				} else {
					break // No match on next character.
				}
				_, _ = rIter.Next() // This won't fail if peek was fine.
			}

			if num == 1 {
				addC = "++ptr;\n"
			} else {
				addC = "ptr += " + strconv.Itoa(num) + ";\n"
			}

		case '<':

			num := 1
			for {
				peeked, err := rIter.Peek()
				if err != nil {
					break // End of the bf.
				}
				if peeked == '<' {
					num += 1
				} else {
					break // No match on next character.
				}
				_, _ = rIter.Next() // This won't fail if peek was fine.
			}

			if num == 1 {
				addC = "--ptr;\n"
			} else {
				addC = "ptr -= " + strconv.Itoa(num) + ";\n"
			}

		case '+':
			num := 1
			for {
				peeked, err := rIter.Peek()
				if err != nil {
					break // End of the bf.
				}
				if peeked == '+' {
					num += 1
				} else {
					break // No match on next character.
				}
				_, _ = rIter.Next() // This won't fail if peek was fine.
			}

			if num == 1 {
				addC = "++*ptr;\n"
			} else {
				addC = "*ptr += " + strconv.Itoa(num) + ";\n"
			}

		case '-':
			num := 1
			for {
				peeked, err := rIter.Peek()
				if err != nil {
					break // End of the bf.
				}
				if peeked == '-' {
					num += 1
				} else {
					break // No match on next character.
				}
				_, _ = rIter.Next() // This won't fail if peek was fine.
			}

			if num == 1 {
				addC = "--*ptr;\n"
			} else {
				addC = "*ptr -= " + strconv.Itoa(num) + ";\n"
			}

		case '.':
			addC = "putchar(*ptr);\n"
		case ',':
			addC = "*ptr = getchar();\n"
		case '[':
			addC = "while (*ptr) {\n"
			indentChange = 1
		case ']':
			addC = "}\n"
			indentLevel -= 1
		default:
			continue
		}

		toAdd := addIndent(indentLevel, addC)
		indentLevel += indentChange
		cSource += toAdd
	}
	cSource += cTail
	return cSource
}

func main() {
	flag.Parse()
	if *cFile == "" {
		panic("No c destination")
	}
	if len(flag.Args()) != 1 {
		panic("No bf source")
	}
	bfFile := (flag.Args())[0]

	bfSource, err := ioutil.ReadFile(bfFile)
	if err != nil {
		panic(err)
	}
	bfString := string(bfSource)

	cSource := makeCSource(bfString)

	outBytes := []byte(cSource)
	err = ioutil.WriteFile(*cFile, outBytes, 0644)
	if err != nil {
		panic(err)
	}
}