alt Hacker NewsNot a good starting type:
type Parser<T> = (input: string) => [T, string]
The article also starts with the concept of a 'partial parser', from which other (non-partial?) parsers can be constructed?
Or, and this is where the real power of partial parsers comes in: we wrap the chain up as a new parser of its own.
(Ironically there is a fitting definition of 'partial' here: the function isn't well defined on all inputs. For some inputs, T is returned, on other inputs, maybe an error is thrown, who knows..)
Replies
> If you combine partial parsers, you end up with a partial parser.
If by partial we mean the parser can fail, not necessarily. optional(elem) and repeat(elem) are total if elem doesn't consume input on error, at least for a reasonable semantics of parser combinators (although we usually consider it a programmer error if elem matches the empty string in repeat(elem)).
Combinators are functional—they always return something. But if you want to return nothing, fine; T is any type. Just return something like unit (ie, the singleton type that has nothing as a value).
Good input. Since we're working in typescript a partial parser can always throw an exception (It's what the parsimmon library does aswell I believe). I decided not to get into those technicalities too much!