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|
package parsec
import (
"bytes"
"fmt"
"strings"
"unicode/utf8"
)
type Parser func(Pointer) (Node, Pointer)
// Parserish types are any type that can be turned into a Parser by Parsify
// These currently include *Parser and string literals.
//
// This makes recursive grammars cleaner and allows string literals to be used directly in most contexts.
// eg, matching balanced paren:
// ```go
// var group Parser
// group = And("(", Maybe(&group), ")")
// ```
// vs
// ```go
// var group ParserPtr{}
// group.P = And(Exact("("), Maybe(group.Parse), Exact(")"))
// ```
type Parserish interface{}
func Parsify(p Parserish) Parser {
switch p := p.(type) {
case func(Pointer) (Node, Pointer):
return Parser(p)
case Parser:
return p
case *Parser:
// Todo: Maybe capture this stack and on nil show it? Is there a good error library to do this?
return func(ptr Pointer) (Node, Pointer) {
return (*p)(ptr)
}
case string:
return Exact(p)
default:
panic(fmt.Errorf("cant turn a `%T` into a parser", p))
}
}
func ParsifyAll(parsers ...Parserish) []Parser {
ret := make([]Parser, len(parsers))
for i, parser := range parsers {
ret[i] = Parsify(parser)
}
return ret
}
func ParseString(parser Parserish, input string) (result Node, remaining string, err error) {
p := Parsify(parser)
result, pointer := p(Pointer{input, 0})
if err, isErr := result.(Error); isErr {
return nil, pointer.Get(), err
}
return result, pointer.Get(), nil
}
func Exact(match string) Parser {
return func(p Pointer) (Node, Pointer) {
if !strings.HasPrefix(p.Get(), match) {
return NewError(p.pos, "Expected "+match), p
}
return match, p.Advance(len(match))
}
}
func Char(match string) Parser {
return func(p Pointer) (Node, Pointer) {
r, w := utf8.DecodeRuneInString(p.Get())
if !strings.ContainsRune(match, r) {
return NewError(p.pos, "Expected one of "+string(match)), p
}
return string(r), p.Advance(w)
}
}
func CharRun(match string) Parser {
return func(p Pointer) (Node, Pointer) {
matched := 0
for p.pos+matched < len(p.input) {
r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
if !strings.ContainsRune(match, r) {
break
}
matched += w
}
if matched == 0 {
return NewError(p.pos, "Expected some of "+match), p
}
return p.input[p.pos : p.pos+matched], p.Advance(matched)
}
}
func CharRunUntil(match string) Parser {
return func(p Pointer) (Node, Pointer) {
matched := 0
for p.pos+matched < len(p.input) {
r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
if strings.ContainsRune(match, r) {
break
}
matched += w
}
if matched == 0 {
return NewError(p.pos, "Expected some of "+match), p
}
return p.input[p.pos : p.pos+matched], p.Advance(matched)
}
}
func Range(r string, repetition ...int) Parser {
min := int(1)
max := int(-1)
switch len(repetition) {
case 0:
case 1:
min = repetition[0]
case 2:
min = repetition[0]
max = repetition[1]
default:
panic(fmt.Errorf("Dont know what %d repetion args mean", len(repetition)))
}
runes := []rune(r)
if len(runes)%3 != 0 {
panic("ranges should be in the form a-z0-9")
}
var ranges [][]rune
for i := 0; i < len(runes); i += 3 {
start := runes[i]
end := runes[i+2]
if start <= end {
ranges = append(ranges, []rune{start, end})
} else {
ranges = append(ranges, []rune{end, start})
}
}
return func(p Pointer) (Node, Pointer) {
matched := 0
for p.pos+matched < len(p.input) {
if max != -1 && matched >= max {
break
}
r, w := utf8.DecodeRuneInString(p.input[p.pos+matched:])
anyMatched := false
for _, rng := range ranges {
if r >= rng[0] && r <= rng[1] {
anyMatched = true
}
}
if !anyMatched {
break
}
matched += w
}
if matched < min {
return NewError(p.pos+matched, fmt.Sprintf("Expected at least %d more of %s", min-matched, r)), p
}
return p.input[p.pos : p.pos+matched], p.Advance(matched)
}
}
func WS(p Pointer) (Node, Pointer) {
_, p2 := CharRun("\t\n\v\f\r \x85\xA0")(p)
return nil, p2
}
func String(quote rune) Parser {
return func(p Pointer) (Node, Pointer) {
var r rune
var w int
r, w = utf8.DecodeRuneInString(p.input[p.pos:])
if r != quote {
return NewError(p.pos, `Expected "`), p
}
matched := w
result := &bytes.Buffer{}
for p.pos+matched < len(p.input) {
r, w = utf8.DecodeRuneInString(p.input[p.pos+matched:])
matched += w
if r == '\\' {
r, w = utf8.DecodeRuneInString(p.input[p.pos+matched:])
result.WriteRune(r)
matched += w
continue
}
if r == quote {
return result.String(), p.Advance(matched)
}
result.WriteRune(r)
}
return NewError(p.pos, "Unterminated string"), p
}
}
|
