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tokens.go
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tokens.go
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package lisp
import (
"fmt"
"regexp"
"strconv"
)
type Tokens []*Token
type tokenType uint8
type Token struct {
typ tokenType
val string
}
type Pattern struct {
typ tokenType
regexp *regexp.Regexp
}
// func (t Token) String() string {
// return fmt.Sprintf("%v", t.val)
// }
func (t *Token) String() string {
return fmt.Sprintf("%v", t.val)
}
const (
whitespaceToken tokenType = iota
commentToken
stringToken
numberToken
openToken
closeToken
symbolToken
)
func (t *Token) Type() string {
switch t.typ {
case commentToken:
return "comment"
case stringToken:
return "string"
case numberToken:
return "number"
case openToken:
return "open"
case closeToken:
return "close"
case symbolToken:
return "symbol"
default:
return "unknown"
}
}
func patterns() []Pattern {
return []Pattern{
{whitespaceToken, regexp.MustCompile(`^\s+`)},
{commentToken, regexp.MustCompile(`^;.*`)},
{stringToken, regexp.MustCompile(`^("(\\.|[^"])*")`)},
{numberToken, regexp.MustCompile(`^((([0-9]+)?\.)?[0-9]+)`)},
{openToken, regexp.MustCompile(`^(\()`)},
{closeToken, regexp.MustCompile(`^(\))`)},
{symbolToken, regexp.MustCompile(`^(:|[^\s();]+)`)},
}
}
func NewTokens(program string) (tokens Tokens) {
for pos := 0; pos < len(program); {
for _, pattern := range patterns() {
if matches := pattern.regexp.FindStringSubmatch(program[pos:]); matches != nil {
if len(matches) > 1 {
tokens = append(tokens, &Token{pattern.typ, matches[1]})
}
pos = pos + len(matches[0])
break
}
}
}
return
}
// Expand until there are no more expansions to do
func (tokens Tokens) Expand() (result Tokens, err error) {
var updated bool
for i := 0; i < len(tokens); i++ {
var start int
quote := Token{symbolToken, ":"}
if *tokens[i] != quote {
result = append(result, tokens[i])
} else {
updated = true
for start = i + 1; *tokens[start] == quote; start++ {
result = append(result, tokens[start])
}
if tokens[i+1].typ == openToken {
if i, err = tokens.findClose(start + 1); err != nil {
return nil, err
}
} else {
i = start
}
result = append(result, &Token{openToken, "("}, &Token{symbolToken, "quote"})
result = append(result, tokens[start:i+1]...)
result = append(result, &Token{closeToken, ")"})
}
}
if updated {
result, err = result.Expand()
}
return
}
func (tokens Tokens) Parse() (cons Cons, err error) {
var pos int
var current *Cons
for pos < len(tokens) {
if current == nil {
cons = Cons{&Nil, &Nil}
current = &cons
} else {
previous_current := current
current = &Cons{&Nil, &Nil}
previous_current.cdr = &Value{consValue, current}
}
t := tokens[pos]
switch t.typ {
case numberToken:
if i, err := strconv.ParseInt(t.val, 10, 0); err != nil {
err = fmt.Errorf("Failed to convert number: %v", t.val)
} else {
current.car = &Value{numberValue, i}
pos++
}
case stringToken:
current.car = &Value{stringValue, t.val[1 : len(t.val)-1]}
pos++
case symbolToken:
current.car = &Value{symbolValue, t.val}
pos++
case openToken:
var nested Cons
start := pos + 1
var end int
if end, err = tokens.findClose(start); err != nil {
return
}
if start == end {
current.car = &Nil
} else {
if nested, err = tokens[start:end].Parse(); err != nil {
return
}
current.car = &Value{consValue, &nested}
}
pos = end + 1
case closeToken:
err = fmt.Errorf("List was closed but not opened")
}
}
return
}
func (t Tokens) findClose(start int) (int, error) {
depth := 1
for i := start; i < len(t); i++ {
t := t[i]
switch t.typ {
case openToken:
depth++
case closeToken:
depth--
}
if depth == 0 {
return i, nil
}
}
return 0, fmt.Errorf("List was opened but not closed")
}