It's a formalization of decorators, I suppose.
at least for the plain
Function instance
It might be possible to create a bifunctor instance for the native
Map too.
Do you care about
Promises at all?
You could probably form a bifunctor over that.
My answer is no (at least for now).
I'll define a Pair type in the test suite to give us a convenient type with which to test.
Just taking a look over the sanctuary-type-classes code now. It looks quite promising.
Okay. It's a modified version of @safareli's gist. It's possible I botched some refactoring. It's also possible the gist is a little off.
What's wrong with it, do you think?
Due to the
while (args.length > 0 && !args[0].done)
It does what I would have expected if it is modified to:
while (args.length > 0 && !args.every(prop('done')))
Or if you'd prefer to not
every over each iteration, it could be refactored to something like:function chainRec(f, x) {
var next = function(x) { return {value: x, done: false}; };
var done = function(x) { return {value: x, done: true}; };
var out = [];
var todo = [x];
while (todo.length > 0) {
var xs = f(next, done, todo.shift());
var partitioned = xs.reduce(function(acc, x) {
var bucket = x.done ? acc[1] : acc[0];
bucket.push(x.value);
return acc;
}, [[], []]);
todo.unshift.apply(todo, partitioned[0]);
out.push.apply(out, partitioned[1]);
}
return out;
}
For example, you can define functions like
forever which will repeatedly run the same action sequentially for any given ChainRec.const forever = m =>
chainRec((next, _, _) => m.map(_ => next(void 0)), void 0);
I just created a
sanctuary tag on Stack Overflow. You may like to subscribe to it. Also, I posted a question: Custom equality semantics for Immutable.js data structures. I'd love to be able to use maps and sets when working with Sanctuary, but for various reasons neither the native types nor the Immutable.js equivalents are currently suitable.
:point_up: September 17, 2016 1:41 PM @scott-christopher are there (more specific) common use cases you could name, to explain it a bit more?
here is test case from Free
for a bit context the Free was not stack safe and for it to be stack safe target monds should have some common interface so that it could depend on it. now we have ChainRec, in purescript it's MonadRec, and Free and other structures could use it for doing safe monadic recursion. if you are interested in that here is a paper about that https://github.com/functorial/stack-safety-for-free/blob/gh-pages/index.markdown