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

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

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
 		}