Merge pull request 'lexer: constants and helpers' (#9)

Reviewed-on: #9

lexer/error.go

@@ -11,8 +11,11 @@ var (
 )
 
 var (
-	// ErrUnacceptableRune indicates the read rune
+	// 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

lexer/lexer.go

@@ -1,6 +1,11 @@
 // 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)
 
@@ -11,7 +16,11 @@ func Run(fn StateFn) error {
 		var err error
 
 		fn, err = fn()
-		if err != nil {
+		switch {
+		case errors.Is(err, io.EOF):
+			// EOF
+			return nil
+		case err != nil:
 			// failed
 			return err
 		}

lexer/position.go

@@ -64,29 +64,3 @@ func (p *Position) StepLine() {
 	p.Line++
 	p.Column = 1
 }
-
-// Next returns a new Position one rune forward
-// on the line
-func (p Position) Next() Position {
-	if p.Line == 0 {
-		p.Reset()
-	}
-
-	return Position{
-		Line:   p.Line,
-		Column: p.Column + 1,
-	}
-}
-
-// NextLine returns a new Position at the begining of the next
-// line.
-func (p Position) NextLine() Position {
-	if p.Line == 0 {
-		p.Reset()
-	}
-
-	return Position{
-		Line:   p.Line + 1,
-		Column: 1,
-	}
-}