The source code appears to be in Text/Megaparsec/Internal.hs, although I haven’t gotten my head around it yet.

I tried a simple example and it seems to work the way I expected.

I’m Glyn Normington. I dipped into Haskell briefly in about 2011, but recently got a little deeper into it when I taught a second year functional programming module at Winchester University, UK. I’m a retired programmer with 39 years experience and try to pass on some general tips in the module. I came here after recently deleting my Reddit account. (I’ve been on the Fediverse for a while as fosstodon.org/@underlap.)