Glasgow Haskell Compiler 7.2.1 released | Hacker News Reader

Glasgow Haskell Compiler 7.2.1 released

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87 pointsJanLaussmann11 comments

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Woohoo, Monad comprehensions :):

http://www.haskell.org/ghc/docs/7.2.1/html/users_guide/synta...

This improve code readability when used judiciously.

What monad would you use them for? I've never seen a really good use case.

Probably the Maybe monad most often, in usual code.

Or really as a shorter way of writing any smaller monadic code blocks.

I really look forward to using this new feature.

I don't know for sure until I try, but I think can be useful for logic monads.

I think LINQ is a special case of a monad comprehension. Syntax checked, type checked, composeable query languages (of which the "Structured" Query Language is only one example) are good things.

So far everywhere where I might have been tempted to use a Maybe monad comprehension, applicative functors were more clear anyhow.

You are right about query languages being a good for for monad comprehensions. See Torston Grust's dissertation[1], specifically "Combinators from Monad Comprehensions."

1. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.88.9...

There is some pretty cool stuff in there for a point release. It's cool that monad comprehensions are back in, but I'm most excited about Safe Haskell, which should enable enable some new types of application (safely running untrusted code).

As I keep telling people, 'Safe Haskell' is not as generally useful as they think it is. Mueval (http://hackage.haskell.org/package/mueval) has to do a lot more than just be careful with its imports before it can safely run arbitrary untrusted code.

Quite relevantly to day-to-day use, ghci's got multiline input and the ability to load up scripts. No more copy-paste out of scratch in emacs!

Good timing, I have haskell exam in 2 hrs ;)

good luck!!! you should have finished it by now! :-)

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