ll1/flexer/flexer.go

package flexer

import "fmt"
import "regexp"
import "strings"
import "strconv"
import . "src.eruta.nl/beoran/ll1/common"

/* Flexer is a flexible regexp and lexeme based
lexer that can be used as an implementation for
generated code.
*/

type BasicToken struct {
	location Location
	kind     Kind
	text     string
	value    Value
}

func (bt BasicToken) Kind() Kind {
	return bt.kind
}

func (bt BasicToken) Location() Location {
	return bt.location
}

func (bt BasicToken) Text() string {
	return bt.text
}

func (bt BasicToken) Value() Value {
	if bt.Value() == nil {
		return StringValue(bt.text)
	} else {
		return bt.value
	}
}

func MakeToken(Location Location, kind Kind, form string,
	args ...interface{}) BasicToken {
	text := fmt.Sprintf(form, args...)
	return BasicToken{Location, kind, text, StringValue(text)}
}

func MakeValueToken(Location Location, kind Kind, value Value) BasicToken {
	text := value.String()
	return BasicToken{Location, kind, text, value}
}

type ErrorToken struct {
	BasicToken
}

func MakeErrorToken(Location Location, form string, args ...interface{}) ErrorToken {
	err := fmt.Errorf(form, args...)
	tok := MakeValueToken(Location, ErrorKind, ErrorValue{err})
	return ErrorToken{tok}
}

func (e ErrorToken) Error() string {
	return fmt.Sprintf("%s%s", e.Location(), e.text)
}

/* Lexeme for Flexer is based on a regular expression.
* While the lexeme may have submatches, the lexer will consume
* the whole match if it matches at the beginning of the current input.
 */
type Lexeme struct {
	Kind
	*regexp.Regexp
	Context string
	Action
}

// DefaultAction is the default action on a match.
// If there is only 1 match, then that is the token,
// otherwise all sub-macthes excluding the first
// whole string match are the tokens.
func DefaultAction(lex Lexer, k Kind, matches ...string) []Token {
	if len(matches) == 1 {
		tok := lex.MakeToken(k, matches[0])
		return []Token{tok}
	}
	res := []Token{}
	for i := 1; 1 < len(matches); i++ {
		tok := lex.MakeToken(k, matches[i])
		res = append(res, tok)
	}
	return res
}

// ContextAction returns an action that returns
// no tokens but switches the lexer context and
// empties the buffer.
func ContextAction(context string) func(lex Lexer, k Kind, matches ...string) []Token {
	return func(lex Lexer, k Kind, matches ...string) []Token {
		lex.PushContext(context)
		lex.Builder().Reset()
		return []Token{}
	}
}

// Returns an action that pops the context and
// returns the token in the buffer with the given kind
func PopAction(kind Kind) func(lex Lexer, k Kind, matches ...string) []Token {
	return func(lex Lexer, k Kind, matches ...string) []Token {
		lex.PopContext()
		tok := lex.MakeBuilderToken(kind)
		return []Token{tok}
	}
}

// Returns an action that stores the match in the lexer buffer.
func StoreAction() func(lex Lexer, k Kind, matches ...string) []Token {
	return func(lex Lexer, k Kind, matches ...string) []Token {
		for _, m := range matches {
			lex.Builder().WriteString(m)
		}
		return []Token{}
	}
}

// Returns an action that stores the match in the lexer buffer after applying UnquoteChar to apply
// an escape sequence.
func EscapeAction(quote byte) func(lex Lexer, k Kind, matches ...string) []Token {
	return func(lex Lexer, k Kind, matches ...string) []Token {
		s, _, t, e := strconv.UnquoteChar(matches[0], quote)
		print("escape", s, t, e)
		if e != nil {
			et := lex.MakeToken(ErrorKind, "%s", e)
			return []Token{et}
		}
		lex.Builder().WriteRune(s)
		lex.Builder().WriteString(t)
		return []Token{}
	}
}

// Try tries to apply a lexeme.
// Returns nil on no match.
func (r Lexeme) Try(lex Lexer) []Token {
	matches := lex.Accept(r.Regexp)
	if matches == nil || len(matches) == 0 {
		return nil
	}
	if r.Action != nil {
		return r.Action(lex, r.Kind, matches...)
	}
	// No action, use default action
	return DefaultAction(lex, r.Kind, matches...)
}

type Flexer struct {
	index    int
	location Location
	lexemes  []Lexeme
	input    string
	name     string
	contexts []string
	builder  strings.Builder
}

func (f Flexer) MakeToken(kind Kind, form string, args ...interface{}) Token {
	return MakeToken(f.location, kind, form, args...)
}

func (f *Flexer) MakeBuilderToken(kind Kind) Token {
	text := f.builder.String()
	f.builder.Reset()
	return f.MakeToken(kind, text)
}

// Advances the flexer to the given index,
// updating the Location.
func (f *Flexer) advanceTo(index int) {
	start := f.index
	end := index
	for i := start; i < end; i++ {
		c := f.input[i] // This works because newlines are ascii.
		if c == '\r' || c == '\n' {
			if c == '\r' && (i+1) < len(f.input) {
				if f.input[i+1] == '\n' {
					i++
				}
			}
			f.location.Line++
			f.location.Col = 1
		} else {
			f.location.Col++
		}
	}
	f.index = end
}

func (f *Flexer) Accept(re *regexp.Regexp) []string {
	indexes := re.FindStringSubmatchIndex(f.input[f.index:len(f.input)])
	if indexes == nil || len(indexes) < 1 {
		return nil
	}
	_, end := f.index+indexes[0], f.index+indexes[1]
	matches := []string{}
	for i := 1; i < len(indexes); i += 2 {
		subStart, subEnd := indexes[i-1]+f.index, indexes[i]+f.index
		sub := f.input[subStart:subEnd]
		matches = append(matches, sub)
	}
	f.advanceTo(end)
	return matches
}

func (f *Flexer) Lexeme(kind Kind, expr, context string, act Action) error {
	re, err := regexp.Compile(`\A` + expr)
	if err != nil {
		return err
	}
	lexeme := Lexeme{kind, re, context, act}
	f.lexemes = append(f.lexemes, lexeme)
	return nil
}

func (f *Flexer) EscapedStringLexeme(kind Kind, first, last, context string) {
	f.Lexeme(SkipKind, first, "", ContextAction(context))
	f.Lexeme(kind, last, context, PopAction(kind))
	f.Lexeme(SkipKind, `\\[etnru][0-9a-f]*`, context, EscapeAction(last[0]))
	f.Lexeme(SkipKind, `.`, context, StoreAction())
}

func (f *Flexer) RawStringLexeme(kind Kind, first, last, context string) {
	f.Lexeme(SkipKind, first, "", ContextAction(context))
	f.Lexeme(kind, last, context, PopAction(kind))
	f.Lexeme(SkipKind, `.`, context, StoreAction())
}

func (f *Flexer) PushContext(context string) {
	f.contexts = append(f.contexts, context)
}

func (f *Flexer) Context() string {
	context := ""
	clen := len(f.contexts)
	if clen > 0 {
		context = f.contexts[clen-1]
	}
	return context
}

func (f *Flexer) PopContext() {
	clen := len(f.contexts)
	if clen > 0 {
		f.contexts = f.contexts[0 : clen-1]
	}
}

func (f *Flexer) Builder() *strings.Builder {
	return &f.builder
}

// Runs the lexer once.
// Return nil if no more progress can be made
func (f *Flexer) LexOnce() []Token {
	for _, lexeme := range f.lexemes {
		if lexeme.Context != f.Context() {
			continue
		}
		tokens := lexeme.Try(f)
		if tokens != nil {
			return tokens
		}
	}
	return nil
}

func (f Flexer) Location() Location {
	return f.location
}

func (f Flexer) EOF() bool {
	return f.index >= len(f.input)
}

func NewFlexer(name, text string) *Flexer {
	res := &Flexer{}
	res.location.Line = 1
	res.location.Col = 1
	res.location.Name = &name
	res.input = text
	return res
}

// KeepToken returns true if the token should be kept
// and false if it is of the kind in the skip list
func KeepToken(tok Token, skips ...Kind) bool {
	for _, skip := range skips {
		if skip == tok.Kind() {
			return false
		}
	}
	return true
}

// Lexes all tokens from the lexer until it reaches
// EOF, or until it cannot progress anymore.
// All tokens in the skip array will be skipped
// from the results.
func LexAll(lex Lexer, skips ...Kind) []Token {
	res := []Token{}
	for !lex.EOF() {
		toks := lex.LexOnce()
		if toks == nil {
			err := lex.MakeToken(ErrorKind, " Lexer error: no lexeme matches. Context:%s.", lex.Context())
			res = append(res, err)
			return res
		}
		for _, tok := range toks {
			if KeepToken(tok, skips...) {
				res = append(res, tok)
			}
		}
	}
	return res
}