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silkapp / rest

Packages for defining APIs, running them, generating client code and documentation.
http://silkapp.github.io/rest
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Simplify, generalize >|< and add >?< #114

Closed bergmark closed 9 years ago

bergmark commented 9 years ago

Generalized the signature of >|<, the error in the first argument is never thrown so we can make that explicit.

>?< is useful in order to write f >?< gorThrowe where f and g give a Maybe result. I added this because I accidentally had f >|< gorThrowe which will never run g if f fails.

hesselink commented 9 years ago

I think the change to >|< is good, the other one I think is too ad-hoc. See my inline comments.

bergmark commented 9 years ago

It is a bit ad-hoc since it's not specific to ExceptT, but it's useful with orThrow, esp since i screwed up and used >|< instead by accident. So I'd argue it's nice to have it clearly defined to prevent confusion.

f >?< gorThrowe = (forThrowe) >|< (gorThrowe) by the way.

We could also publish this module as a separate package (we already have that internally), but I suppose that doesn't answer the question about defining >?< in it.

hesselink commented 9 years ago

I don't see how this would prevent you from using >|<... What you really want is <|> and MaybeT. With ExceptT we really also want <|>, but that requires a Monoid on e, which is why we made >|<, but I think for Maybe return values, you can just use MaybeT at the use site. Is this so common it needs a special combinator?

bergmark commented 9 years ago

I guess I can't tell that yet, I'll leave it out for now.

Pushed >|< changes 72b8ae89a27d6cad194ef086c74a7a7f94fc6fa3