lexer: introduce Accept()/AcceptAll() helpers

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

lexer/lexer.go

@@ -1,2 +1,54 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
+
+import "io"
+
+// 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
+		}
+	}
+}

readcloser.go

@@ -1,64 +0,0 @@
-package core
-
-import (
-	"bytes"
-	"io"
-	"io/fs"
-	"strings"
-)
-
-// ReadCloser adds a Close() to Readers without one
-type ReadCloser struct {
-	r io.Reader
-}
-
-// Read passes the Read() call to the underlying [io.Reader]
-// and fail if it was Closed()
-func (rc *ReadCloser) Read(b []byte) (int, error) {
-	switch {
-	case rc.r != nil:
-		return rc.r.Read(b)
-	default:
-		return 0, fs.ErrClosed
-	}
-}
-
-// Close attempts to Close the underlying [io.Reader], or
-// remove it if it doesn't support Close() and fail
-// if closed twice
-func (rc *ReadCloser) Close() error {
-	switch {
-	case rc.r != nil:
-		rc.r = nil
-		return nil
-	default:
-		return fs.ErrClosed
-	}
-}
-
-// NewReadCloser wraps a [io.Reader] to satisfy
-// [io.ReadCloser] if needed
-func NewReadCloser(r io.Reader) io.ReadCloser {
-	switch p := r.(type) {
-	case io.ReadCloser:
-		return p
-	case nil:
-		return nil
-	default:
-		return &ReadCloser{
-			r: r,
-		}
-	}
-}
-
-// NewReadCloserBytes wraps a bytes slice to implement
-// a [io.ReadCloser]
-func NewReadCloserBytes(b []byte) io.ReadCloser {
-	return NewReadCloser(bytes.NewReader(b))
-}
-
-// NewReadCloserString wraps a string to implement
-// a [io.ReadCloser]
-func NewReadCloserString(s string) io.ReadCloser {
-	return NewReadCloser(strings.NewReader(s))
-}

runes/docs.go

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

runes/reader.go

@@ -1,8 +1,7 @@
-package lexer
+package runes
 
 import (
 	"bytes"
-	"errors"
 	"io"
 	"strings"
 	"unicode/utf8"
@@ -19,14 +18,7 @@ const (
 
 // implemented interfaces
 var (
-	_ io.RuneReader  = (*Reader)(nil)
+	_ io.RuneReader = (*Reader)(nil)
-	_ io.RuneScanner = (*Reader)(nil)
-)
-
-var (
-	// ErrInvalidUnreadRune indicates UnreadRune() was calls after an
-	// action other than a successful ReadRune()
-	ErrInvalidUnreadRune = errors.New("invalid UnreadRune() call")
 )
 
 // Reader is a RuneReader aimed at implementing text parsers
@@ -36,8 +28,6 @@ type Reader struct {
 	buf    []byte
 	off    int
 	cursor int
-
-	lastRuneSize int
 }
 
 // String returns what's already Read but not yet emitted or discarded
@@ -64,9 +54,6 @@ func (b *Reader) Discard() {
 		// step
 		b.off = b.cursor
 	}
-
-	// and prevent UnreadRune()
-	b.lastRuneSize = -1
 }
 
 // ready tells how many bytes are ready to decode
@@ -152,8 +139,6 @@ func (b *Reader) ReadRune() (rune, int, error) {
 	for {
 		err := b.needsBytes(count)
 		if err != nil {
-			b.lastRuneSize = -1
-
 			return 0, 0, err
 		}
 
@@ -168,36 +153,9 @@ func (b *Reader) ReadRune() (rune, int, error) {
 
 	// decode rune
 	r, l := utf8.DecodeRune(b.buf[b.cursor:])
-	// step over
-	b.cursor += l
-	// and remember for UnreadRune()
-	b.lastRuneSize = l
-
 	return r, l, nil
 }
 
-// UnreadRune moves the cursor where it was before the last call to ReadRune
-func (b *Reader) UnreadRune() error {
-	if b.lastRuneSize > 0 {
-		b.cursor -= b.lastRuneSize
-		b.lastRuneSize = -1
-		return nil
-	}
-
-	return ErrInvalidUnreadRune
-}
-
-// PeekRune returns information about the next rune without moving the
-// cursor
-func (b *Reader) PeekRune() (rune, int, error) {
-	r, l, err := b.ReadRune()
-	if err != nil {
-		return r, l, err
-	}
-	err = b.UnreadRune()
-	return r, l, err
-}
-
 // NewReader creates a new runes [Reader] using the given [io.Reader]
 func NewReader(r io.Reader) *Reader {
 	if r == nil {