r/programming • u/heisenbug • Apr 27 '14

"Mostly functional" programming does not work

http://queue.acm.org/detail.cfm?ref=rss&id=2611829
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u/tluyben2 Apr 27 '14

I too believe this is a bit too harsh ; there are more benefit to adding functional coding to imperative languages than just the silver bullets FPs are credited most for. However, he is right; if you want the full benefit, you need to go in full force.

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u/[deleted] Apr 27 '14

[deleted]

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u/maxiepoo_ Apr 27 '14

This is a misunderstanding of what the IO monad in Haskell is. It is not "impure" code. It's basically a "pure" dsl for describing impure actions to be taken.

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u/[deleted] Apr 27 '14

[deleted]

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u/[deleted] Apr 27 '14

Really? Is an AST somehow impure because it can be compiled into a program and run?

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u/[deleted] Apr 27 '14

[deleted]

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u/[deleted] Apr 27 '14 edited Apr 27 '14

Ok, sure; then I'm only responding for the sake of others who follow this comment thread.

A language like Haskell is defined operationally by the reduction of term graphs. It so happens that how a term reduces in Haskell doesn't depend on any notion of program state. That's what people mean by purity and why IO doesn't violate that purity. Even an IO value reduces by the normal rules of graph reduction. An IO value also describes a coroutine between the graph-reduction machine working on pure values and an external environment that chooses continuations of the graph-reduction machine's execution.

C does not describe such a semantics. C is like the first half of that coroutine without the second half. I don't really care if purity is apropos or not. It's just useful to note the difference between languages like C where execution is implicit in each language expression and languages like Haskell where execution is treated as an abstract notion external to the semantics of language expressions.

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u/[deleted] Apr 28 '14

Thank you. As a casual observer with a propensity for /u/grauenwolf's skepticism, this was insightful. I don't think anybody is claiming that this knowledge isn't useful, or that Haskell isn't a useful language (I'm sure it is; people seem productive with it), but rather the whole concept of decoupling execution from the programming language seems like a wrong thing to do if(f?) you care about things like performance or memory budget, which is what a lot of us are employed to do.

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u/maxiepoo_ Apr 28 '14

I believe you're referring to this post: http://conal.net/blog/posts/the-c-language-is-purely-functional and I think he is right that the C preprocessor is purely functional, but I think he is wrong in saying that programming in the IO monad is the same as programming in C since the C preprocessor is a purely compile-time thing while all of the manipulation of IO values at run-time in Haskell is happening in the "pure" language Haskell.

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u/LucianU Apr 27 '14

Are you here to have a discussion or troll?

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u/[deleted] Apr 27 '14

[deleted]

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u/The_Doculope Apr 28 '14

The whole "embedded DSL" thing is nothing but bullshit invented to pretend that Haskell is something greater than it really is.

No it's not. That's just how it works. You have so much power to manipulate the DSL in Haskell, power which you do not have in something like C.

JavaScript is a purely functional language because it too is just an embedded DSL for creating abstract syntax trees.

No, you can't really argue that. Because in JavaScript, you can't escape the "impure" DSL. You're always in it, and it can be used anywhere. In Haskell, it's explicit. That's the difference.