lexer: introduce Position.Next()/Position.NextLine() factories

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

lexer/error.go

@@ -1,6 +1,7 @@
 package lexer
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 )
@@ -9,6 +10,11 @@ var (
 	_ error = (*Error)(nil)
 )
 
+var (
+	// ErrUnacceptableRune indicates the read rune
+	ErrUnacceptableRune = errors.New("rune not acceptable in context")
+)
+
 // Error represents a generic parsing error
 type Error struct {
 	Filename string

lexer/lexer.go

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

lexer/position.go

@@ -64,3 +64,29 @@ 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,
+	}
+}