A predicate on the parser result and the user state. This function must return true if the input fulfills the predicate, or failure information object if it does not. Returning things other than true will make it behave like a failure.
true
A predicate on the parser result and the user state. This function must return
trueif the input fulfills the predicate, or failure information object if it does not. Returning things other thantruewill make it behave like a failure.