Re: [Haskell-cafe] Language complexity & beginners (Was: New type of ($) operator in GHC 8.0 is problematic)

This doesn't really work in a non-strict language like Haskell with uncontrolled recursion. We often need a lazy int that may be _|_ and shouldn't affect termination of the program unless demanded. The result would be that you'd actually have to compile all of your code several ways times the number of type arguments and you'd get rather severely different semantics around evaluation as it switched between strictness and laziness. Moreover, cycles that happened to involve one of these values would have to tie the knot strictly, meaning you'd have issues like scheme where letrec secretly exposes extra, observable, #f cases when you encounter a cycle. -Edward On Sun, Feb 7, 2016 at 7:17 AM, Ben Lippmeier wrote:

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On 7 Feb 2016, at 9:50 pm, Joachim Durchholz wrote:

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For the Int/Int# concept, the approaches I have seen either ignore the efficiency and let the machine figure out what to do (Smalltalk, Python, pre-Int# Haskell), or they complicate the type system at the expense of polymorphism (Java, Eiffel), or they complicate the type system even more to regain some form of polymorphism (C++, today's Haskell).

Although I haven’t implemented it, I suspect another approach is to just specialise every polymorphic function at its unboxed type arguments. Boxed and unboxed value types would share the same kind. Of course, full specialisation of polymorphic code assumes that code is available in the interface files, but we’ve almost got that already. Dealing with mutual recursion could be a pain, though.

I don’t think specialisation was an option back when unboxed types were originally implemented. I believe GHC’s support for cross module inlining came some time after the unboxed types, if the publication dates of the relative papers are to be a guide.

Ben.

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