lexer: introduce Error{}

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

README.md

@@ -1,78 +1 @@
 # asciigoat's core library
-
-[![Go Reference][godoc-badge]][godoc]
-[![Go Report Card][goreport-badge]][goreport]
-
-This package contains the basics for writing simple parsers of
-text languages heavily inspired by
-[Rob Pike](https://en.wikipedia.org/wiki/Rob_Pike)'s talk on
-[Lexical Scanning in Go](https://go.dev/talks/2011/lex.slide#1) in 2011 which
-you can [watch online](https://www.youtube.com/watch?v=HxaD_trXwRE) to get
-better understanding of the ideas behind **asciigoat**.
-
-**asciigoat** is [MIT](https://opensource.org/license/mit/) licensed.
-
-[godoc]: https://pkg.go.dev/asciigoat.org/core
-[godoc-badge]: https://pkg.go.dev/badge/asciigoat.org/core.svg
-[goreport]: https://goreportcard.com/report/asciigoat.org/core
-[goreport-badge]: https://goreportcard.com/badge/asciigoat.org/core
-
-[godoc-lexer-reader]: https://pkg.go.dev/asciigoat.org/core/lexer#Reader
-[godoc-readcloser]: https://pkg.go.dev/asciigoat.org/core#ReadCloser
-
-## Lexer
-
-### lexer.Reader
-
-The lexer package provides [`lexer.Reader`][godoc-lexer-reader] which is
-actually an [`io.RuneScanner`](https://pkg.go.dev/io#RuneScanner)
-that buffers accepted runes until you are ready to
-[emit](https://pkg.go.dev/asciigoat.org/core/lexer#Reader.Emit) or
-[discard](https://pkg.go.dev/asciigoat.org/core/lexer#Reader.Discard).
-
-### lexer.Position
-
-[`lexer.Position`](https://pkg.go.dev/asciigoat.org/core/lexer#Position)
-is a `(Line, Column)` pair with methods to facilitate tracking
-your position on the source [Reader](https://pkg.go.dev/io#Reader).
-
-### lexer.Error
-
-[`lexer.Error`](https://pkg.go.dev/asciigoat.org/core/lexer#Error)
-is an [unwrappable](https://pkg.go.dev/errors#Unwrap) error with a
-token position and hint attached.
-
-### lexer.StateFn
-
-At the heart of **asciigoat** we have _state functions_ as proposed on [Rob Pike's famous talk](https://www.youtube.com/watch?v=HxaD_trXwRE) which return the next _state function_ parsing is done.
-Additionally there is a [`Run()`](https://pkg.go.dev/asciigoat.org/lexer#Run) helper that implements the loop.
-
-### rune checkers
-
-_Rune checkers_ are simple functions that tell if a rune is of a class or it's not.
-Fundamental checkers are provided by the [`unicode` package](https://pkg.go.dev/unicode).
-
-Our [`lexer.Reader`][godoc-lexer-reader] uses them on its `Accept()` and `AcceptAll()` methods to
-make it easier to consume the _source_ document.
-
-To facilitate the declaration of _rune classes_ in the context of **asciigoat** powered parsers we include
-a series of rune checker factories.
-
-* `NewIsIn(string)`
-* `NewIsInRunes(...rune)`
-* `NewIsNot(checker)`
-* `NewIsOneOf(...checker)`
-
-## Others
-
-### ReadCloser
-
-[ReadCloser][godoc-readcloser] assists in providing a
-[io.Closer](https://pkg.go.dev/io#Closer) to Readers or buffers without on,
-or unearthing one if available so
-[io.ReadCloser](https://pkg.go.dev/io#ReadCloser) can be fulfilled.
-
-## See also
-
-* [asciigoat.org/ini](https://asciigoat.org/ini)
-* [oss.jpi.io](https://oss.jpi.io)

lexer/error.go

@@ -1,7 +1,6 @@
 package lexer
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 )
@@ -10,14 +9,6 @@ var (
 	_ error = (*Error)(nil)
 )
 
-var (
-	// ErrUnacceptableRune indicates the read rune isn't acceptable in the context
-	ErrUnacceptableRune = errors.New("rune not acceptable in context")
-
-	// ErrNotImplemented indicates something hasn't been implemented yet
-	ErrNotImplemented = errors.New("not implemented")
-)
-
 // Error represents a generic parsing error
 type Error struct {
 	Filename string

lexer/lexer.go

@@ -1,31 +1,17 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
 
-import (
-	"errors"
-	"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 {
-	for fn != nil {
-		var err error
+	var err error
 
+	for fn != nil && err == nil {
 		fn, err = fn()
-		switch {
-		case errors.Is(err, io.EOF):
-			// EOF
-			return nil
-		case err != nil:
-			// failed
-			return err
-		}
 	}
 
-	// ended
-	return nil
+	return err
 }

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,
+	}
 }

lexer/runes.go

@@ -1,47 +0,0 @@
-package lexer
-
-import (
-	"strings"
-	"unicode"
-)
-
-// NewIsNot generates a rune condition checker that reverses the
-// decision of the given checker.
-func NewIsNot(cond func(rune) bool) func(rune) bool {
-	return func(r rune) bool {
-		return !cond(r)
-	}
-}
-
-// NewIsIn generates a rune condition checker that accepts runes
-// contained on the provided string
-func NewIsIn(s string) func(rune) bool {
-	return func(r rune) bool {
-		return strings.ContainsRune(s, r)
-	}
-}
-
-// NewIsInRunes generates a rune condition checker that accepts
-// the runes specified
-func NewIsInRunes(s ...rune) func(rune) bool {
-	return NewIsIn(string(s))
-}
-
-// NewIsOneOf generates a run condition checker that accepts runes
-// accepted by any of the given checkers
-func NewIsOneOf(s ...func(rune) bool) func(rune) bool {
-	return func(r rune) bool {
-		for _, cond := range s {
-			if cond(r) {
-				return true
-			}
-		}
-		return false
-	}
-}
-
-// IsSpace reports whether the rune is a space character as
-// defined by Unicode's White Space property
-func IsSpace(r rune) bool {
-	return unicode.IsSpace(r)
-}