lexer: to simplify states, Lexer.EmitError() assumes EOF if nil is passed

Signed-off-by: Alejandro Mery <amery@jpi.io>

lexer/lexer.go

@@ -0,0 +1,126 @@
+package lexer
+
+import (
+	"errors"
+	"fmt"
+
+	"asciigoat.org/core/runes"
+)
+
+// state function
+type StateFn func(Lexer) StateFn
+
+type Lexer interface {
+	Run() // run state machine
+
+	Position() TokenPosition // base for the next token
+	Tokens() <-chan Token    // tokens output
+
+	AtLeast(n int) ([]rune, error)
+
+	NewLine()
+	Step(n int)
+
+	Emit(TokenType)
+	EmitError(error)
+	EmitErrorf(string, ...interface{})
+	EmitSyntaxError(string, ...interface{})
+}
+
+type lexer struct {
+	start StateFn // initial state
+
+	in     *runes.Feeder // runes source
+	pos    TokenPosition // base for the next token
+	cursor int           // look ahead pointer
+	tokens chan Token    // tokens output
+}
+
+func NewLexer(start StateFn, in *runes.Feeder, tokens int) Lexer {
+	return &lexer{
+		start:  start,
+		in:     in,
+		pos:    TokenPosition{1, 1},
+		tokens: make(chan Token, tokens),
+	}
+}
+
+func (lex *lexer) Run() {
+	defer close(lex.tokens)
+
+	for state := lex.start; state != nil; {
+		state = state(lex)
+	}
+}
+
+func (lex *lexer) AtLeast(n int) ([]rune, error) {
+	min := lex.cursor
+	if n > 0 {
+		min += n
+	}
+
+	s, err := lex.in.AtLeast(min)
+	if len(s) > lex.cursor {
+		s = s[lex.cursor:]
+	} else {
+		s = nil
+	}
+	return s, err
+}
+
+func (lex *lexer) Position() TokenPosition {
+	return lex.pos
+}
+
+func (lex *lexer) Step(n int) {
+	lex.cursor += n
+}
+
+func (lex *lexer) NewLine() {
+	lex.pos.NewLine()
+}
+
+func (lex *lexer) Tokens() <-chan Token {
+	return lex.tokens
+}
+
+func (lex *lexer) Emit(typ TokenType) {
+	var text []rune
+
+	pos := lex.pos
+
+	// extract text to emit, and update cursor for the next
+	if n := lex.cursor; n > 0 {
+		text = lex.in.Runes()[:n]
+		lex.in.Skip(n)
+		lex.pos.Step(n)
+		lex.cursor = 0
+	}
+
+	lex.tokens <- NewToken(typ, text, pos)
+}
+
+func (lex *lexer) EmitError(err error) {
+	// if no error is passed, assume they mean EOF
+	if err == nil {
+		err = EOF
+	}
+
+	lex.tokens <- NewErrorToken(err, lex.pos)
+}
+
+func (lex *lexer) EmitErrorf(s string, args ...interface{}) {
+	if len(args) > 0 {
+		s = fmt.Sprintf(s, args...)
+	}
+
+	lex.tokens <- NewErrorToken(errors.New(s), lex.pos)
+}
+
+func (lex *lexer) EmitSyntaxError(s string, args ...interface{}) {
+	if len(args) > 0 {
+		s = fmt.Sprintf(s, args...)
+	}
+
+	lex.tokens <- NewSyntaxErrorToken(s, lex.pos, lex.cursor, lex.in.Runes())
+}

lexer/token.go

@@ -0,0 +1,125 @@
+package lexer
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+var (
+	EOF = io.EOF // EOF marker
+)
+
+// Token type
+type TokenType int
+
+const (
+	TokenError TokenType = iota
+)
+
+// Token Position
+type TokenPosition struct {
+	Line int
+	Row  int
+}
+
+func (pos *TokenPosition) Reset() {
+	pos.Line = 1
+	pos.Row = 1
+}
+
+func (pos *TokenPosition) Step(n int) {
+	pos.Row += n
+}
+
+func (pos *TokenPosition) NewLine() {
+	pos.Line += 1
+	pos.Row = 1
+}
+
+// Token
+type Token interface {
+	Type() TokenType
+	String() string
+	Position() TokenPosition
+}
+
+type token struct {
+	typ TokenType
+	pos TokenPosition
+	val string
+}
+
+func NewToken(typ TokenType, val []rune, pos TokenPosition) Token {
+	return &token{
+		typ: typ,
+		val: string(val),
+		pos: pos,
+	}
+}
+
+func (t token) Type() TokenType {
+	return t.typ
+}
+
+func (t token) Position() TokenPosition {
+	return t.pos
+}
+
+func (t token) String() string {
+	return t.val
+}
+
+// ErrorToken
+type ErrorToken interface {
+	Token
+	Error() string
+	Unwrap() error
+}
+
+type errorToken struct {
+	token
+	err error
+}
+
+func NewErrorToken(err error, pos TokenPosition) ErrorToken {
+	return &errorToken{
+		token: token{
+			typ: TokenError,
+			val: err.Error(),
+			pos: pos,
+		},
+		err: err,
+	}
+}
+
+func (t errorToken) Error() string {
+	return t.err.Error()
+}
+
+func (t errorToken) Unwrap() error {
+	return t.err
+}
+
+// SyntaxErrorToken
+type SyntaxErrorToken struct {
+	ErrorToken
+
+	Cursor int
+	Buffer string
+}
+
+func NewSyntaxErrorToken(msg string, pos TokenPosition, cur int, buffer []rune) *SyntaxErrorToken {
+	s := fmt.Sprintf("Syntax Error at %v.%v+%v", pos.Line, pos.Row, cur)
+
+	if len(msg) > 0 {
+		s = fmt.Sprintf("%s: %s", s, msg)
+	}
+
+	return &SyntaxErrorToken{
+		ErrorToken: NewErrorToken(errors.New(s), pos),
+
+		Cursor: cur,
+		Buffer: string(buffer),
+	}
+}