Re-implement sep_by in terms of and_then

1 files changed, 5 insertions, 3 deletions

diff --git a/src/parcom/parser.cr b/src/parcom/parser.cr
index d13219d..7a06f53 100644
--- a/src/parcom/parser.cr
+++ b/src/parcom/parser.cr
@@ -303,6 +303,7 @@ module Parcom
         values = [] of U
         r = self.parse?(tokens)
         until r.nil?
+          # Stop if the parser didn't consume any input
           break unless tokens != r.tokens
           tokens = r.tokens
           values << r.value
@@ -439,9 +440,10 @@ module Parcom
     # instance of `self`. It will succeed if it can parse an instance of `self`
     # that is not followed by any `sep` instances.
     def sep_by(sep : Parser(T, _)) : Parser(T, Array(U))
-      (self + (sep >> self).many).map do |head, tail|
-        tail.unshift(head)
-      end.named("<#{@name}> sep by <#{sep.name}>")
+      parser_chain "<#{@name}> sep by <#{sep.name}>", T, Array(U),
+        {head, self},
+        {tail, (sep >> self).many},
+        finally: Parser(T, Array(U)).pure(tail.unshift(head))
     end
   end
 end