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
 		}