asajeffrey / parsell Goto Github PK

The type for and_then should be that it Cow's p's output. For instance:

   let p = character(char::is_alphabetic).plus().buffer();
   let q = character(char::is_numeric).star().buffer();
   p.and_then(q).parse("abc1").unContinue().parse("23!")

should return (Owned(String::from("abc")),Owned(String::from("123"))). At the moment. "abc" is borrowed rather than owned, which is producing lifetime issues.

At the moment, committed parsers call init() to create a stateful parser. For boxed parers, this usually means calling Box::new(parser.init().boxable()), so we are boxing the parser every time it is initialized. It would be better to call init_parse, which avoid boxing the parser unless we need to save its state.

Really, the interface should be an applicative functor. The idea would be:

interface Parser { ... fn apply<P>(self, p: P) -> Apply<Self, P> { ... } ... }
impl<P,Q,Str> Uncommitted<Str> for Apply<P,Q> 
    where P: Uncommitted<Str>,
          Q: Committed<Str>,
          P::Output: Function<Q::Output>, 
{ ... }

so you could write something like:

character(...).emitting(myfun).apply(this).apply(that);

This would support Kleene Star as well, with something like:

interface Parser { ... fn apply_star<P>(self, p: P) -> ApplyStar<Self, P> { ... } ... }
impl<P,Q,Str> Uncommitted<Str> for ApplyStar<P,Q> 
    where P: Uncommitted<Str>,
          Q: Uncommitted<Str>,
          P::Output: Function<Q::Output, Output = P::Output>, 
{ ... }

For example, the current p.star(f) would be:

emit(f).apply_star(p)

and the current p.plus(f) would be:

p.map(|x| f().apply(x)).apply_star(p)

this uses F: FnOnce(X) -> F as a replacement for Consumer<F>.

As far as I can find, the only examples are the ones in the readme. If there is a more comprehensive set of them, a link to them should be added to the readme as well. Even the tests are more or less empty

It would be nice to get a type error from p.and_then(q) in the case that q isn't committed. At the moment the type error isn't until much later, and is pretty incomprehensible.

We should be able to discard results easily, with something like p.discard_and_then(q), p.and_then_discard(q) etc.

The library takes a lot of time to typecheck, for example travis (https://travis-ci.org/asajeffrey/parsell/builds/107310315) reports 1 min 15 sec for stable, 2 min 46 sec for beta and 3 min 41 sec for nightly.