The only differences between a Plain and a Lazy parser are the instance of Applicative, and the type (and implementation) of runParser. We therefore need to newtype the original Parser type, to allow it to have a different instance.

A return type like Either, that distinguishes not only between right and wrong answers, but also has commitment, so that a failure cannot be undone. This should only be used for writing very primitive parsers - really it is an internal detail of the library. The z type is the remaining unconsumed input.

Apply a parser to an input token sequence.

Simply return the next token in the input tokenstream.

Succeed if the end of file/input has been reached, fail otherwise.

Return the next token if it satisfies the given predicate.

Return the next token if it satisfies the given predicate. The String argument describes the predicate for better error messages.

p onFail q means parse p, unless p fails, in which case parse q instead. Can be chained together to give multiple attempts to parse something. (Note that q could itself be a failing parser, e.g. to change the error message from that defined in p to something different.) However, a severe failure in p cannot be ignored.

Push some tokens back onto the front of the input stream and reparse. This is useful e.g. for recursively expanding macros. When the user-parser recognises a macro use, it can lookup the macro expansion from the parse state, lex it, and then stuff the lexed expansion back down into the parser.