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

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

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

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