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/position.go

@@ -41,6 +41,30 @@ func (p *Position) Step() {
 	p.Column++
 }
 
+// StepN moves the column N places forward
+func (p *Position) StepN(n int) {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	switch {
+	case n > 0:
+		p.Column += n
+	default:
+		panic(fmt.Errorf("invalid %v increment", n))
+	}
+}
+
+// StepLine moves position to the start of the next line
+func (p *Position) StepLine() {
+	if p.Line == 0 {
+		p.Reset()
+	}
+
+	p.Line++
+	p.Column = 1
+}
+
 // Next returns a new Position one rune forward
 // on the line
 func (p Position) Next() Position {