Symparsec.Parser.Or

Choice operator. Try left; if it fails, try right.

This is a problematic combinator:

• Implementation is clumsy due to internal parser state being untouchable. We must record seen characters, in order to replay them on the right parser in case the left parser fails.
• Errors degrade due to left parser errors being discarded. Perhaps your string was one character off a successful left parse; but if it fails, you won't see that error.
• It's hard to reason about. It might break in certain situations.

Documentation

type family pl :<|>: pr where ... infixl 3

Parser choice. Try left; if it fails, backtrack and try right.

Be warned that this parser is experimental, and likely brittle. If possible, consider designing your schema to permit non-backtracking parsing. Or if not, have both sides always parse the same length, in which case this parser should probably work fine.

Equations

'(plCh, plEnd, sl) :<|>: '(prCh, prEnd, sr) = '(OrChSym plCh prCh sr, OrEndSym plEnd prCh prEnd sr, Left '(sl, '[]))