lexer: create Lexer factories for io.Reader, []byte and string

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

lexer/error.go

@@ -1,45 +0,0 @@
-package lexer
-
-import (
-	"fmt"
-	"strings"
-)
-
-var (
-	_ error = (*Error)(nil)
-)
-
-// Error represents a generic parsing error
-type Error struct {
-	Filename string
-	Line     int
-	Column   int
-
-	Content string
-	Err     error
-}
-
-func (err Error) Error() string {
-	var s []string
-
-	switch {
-	case err.Line > 0 || err.Column > 0:
-		s = append(s, fmt.Sprintf("%s:%v:%v", err.Filename, err.Line, err.Column))
-	case err.Filename != "":
-		s = append(s, err.Filename)
-	}
-
-	if err.Err != nil {
-		s = append(s, err.Err.Error())
-	}
-
-	if err.Content != "" {
-		s = append(s, fmt.Sprintf("%q", err.Content))
-	}
-
-	return strings.Join(s, ": ")
-}
-
-func (err Error) Unwrap() error {
-	return err.Err
-}

lexer/lexer.go

@@ -1,2 +1,106 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
+
+import (
+	"io"
+
+	"asciigoat.org/core/runes"
+)
+
+// Lexer adds Accept and AcceptAll support to a
+// [io.RuneScanner]
+type Lexer struct {
+	io.RuneScanner
+}
+
+// Accept consumes a rune from the source if it meets the condition.
+// it returns true if the condition was met and false if it wasn't.
+func (p Lexer) Accept(cond func(rune) bool) bool {
+	return Accept(p, cond)
+}
+
+// AcceptAll consumes runes from the source as long as they meet the
+// condition. it returns true if the condition was met for at least one rune,
+// and false if it wasn't.
+func (p Lexer) AcceptAll(cond func(rune) bool) bool {
+	return AcceptAll(p, cond)
+}
+
+// NewLexer extends a [io.RuneScanner] with Accept()/AcceptAll()
+// functionality
+func NewLexer(src io.RuneScanner) *Lexer {
+	if src == nil {
+		return nil
+	}
+
+	return &Lexer{src}
+}
+
+// NewLexerReader creates a Lexer from an [io.Reader]
+func NewLexerReader(r io.Reader) *Lexer {
+	if r == nil {
+		return nil
+	}
+
+	return &Lexer{runes.NewReader(r)}
+}
+
+// NewLexerBytes creates a Lexer from raw bytes
+func NewLexerBytes(b []byte) *Lexer {
+	return &Lexer{runes.NewReaderBytes(b)}
+}
+
+// NewLexerString creates a Lexer from a data string
+func NewLexerString(s string) *Lexer {
+	return &Lexer{runes.NewReaderString(s)}
+}
+
+// StateFn is a State Function of the parser
+type StateFn func() (StateFn, error)
+
+// Run runs a state machine until the state function either
+// returns nil or an error
+func Run(fn StateFn) error {
+	var err error
+
+	for fn != nil && err == nil {
+		fn, err = fn()
+	}
+
+	return err
+}
+
+// Accept consumes a rune from the source if it meets the condition.
+// it returns true if the condition was met and false if it wasn't.
+func Accept(src io.RuneScanner, cond func(r rune) bool) bool {
+	r, _, err := src.ReadRune()
+	switch {
+	case err != nil:
+		return false
+	case cond(r):
+		return true
+	default:
+		_ = src.UnreadRune()
+		return false
+	}
+}
+
+// AcceptAll consumes runes from the source as long as they meet the
+// condition. it returns true if the condition was met for at least one rune,
+// and false if it wasn't.
+func AcceptAll(src io.RuneScanner, cond func(r rune) bool) bool {
+	var accepted bool
+
+	for {
+		r, _, err := src.ReadRune()
+		switch {
+		case err != nil:
+			return accepted
+		case cond(r):
+			accepted = true
+		default:
+			_ = src.UnreadRune()
+			return accepted
+		}
+	}
+}

lexer/position.go

@@ -41,26 +41,28 @@ func (p *Position) Step() {
 	p.Column++
 }
 
-// StepN moves the column N places forward
-func (p *Position) StepN(n int) {
+// Next returns a new Position one rune forward
+// on the line
+func (p Position) Next() Position {
 	if p.Line == 0 {
 		p.Reset()
 	}
 
-	switch {
-	case n > 0:
-		p.Column += n
-	default:
-		panic(fmt.Errorf("invalid %v increment", n))
+	return Position{
+		Line:   p.Line,
+		Column: p.Column + 1,
 	}
 }
 
-// StepLine moves position to the start of the next line
-func (p *Position) StepLine() {
+// NextLine returns a new Position at the begining of the next
+// line.
+func (p Position) NextLine() Position {
 	if p.Line == 0 {
 		p.Reset()
 	}
 
-	p.Line++
-	p.Column = 1
+	return Position{
+		Line:   p.Line + 1,
+		Column: 1,
+	}
 }

runes/docs.go

@@ -0,0 +1,2 @@
+// Package runes helps us work with runes
+package runes

runes/reader.go

@@ -1,4 +1,4 @@
-package lexer
+package runes
 
 import (
 	"bytes"