Merge pull request #131 from inhabitedtype/advance-check

advance-check: parser should fail on negative inputs
inhabitedtype · Jan 24, 2018 · 838f53c · 838f53c
2 parents 595ec59 + dabd476
commit 838f53c
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/lib/angstrom.ml b/lib/angstrom.ml
@@ -228,7 +228,9 @@ let end_of_input =
     | false -> fail "end_of_input"
 
 let advance n =
-  { run = fun input pos more _fail succ -> succ input (pos + n) more () }
+  if n < 0
+  then fail "advance"
+  else { run = fun input pos more _fail succ -> succ input (pos + n) more () }
 
 let pos =
   { run = fun input pos more _fail succ -> succ input pos more pos }