Karl Voelker wrote:

On Sun, Mar 15, 2015, at 09:17 AM, Simon Kitching wrote:

And AIUI the Haskell compiler/runtime can postpone evaluation of any function (laziness), or reorder function calls whever it thinks this good.

It's not that it "can" but that it must. Haskell's evaluation strategy
is a part of the language specification.

Consider this expression:

let f = 1 : f in take 5 f

You can paste this into ghci and feel confident that it's going to
terminate. You're not at the whim of the runtime.

I think you may find these articles interesting:

https://wiki.haskell.org/Lazy_evaluation
https://wiki.haskell.org/Non-strict_semantics

Strictly speaking, the Haskell language standard only specifies that Haskell has non-strict semantics, not that it needs to be evaluated using lazy evaluation.

Of course, the two are related. I have tried to expand on the details here:

  https://hackhands.com/non-strict-semantics-haskell


Best regards,
Heinrich Apfelmus

--
http://apfelmus.nfshost.com

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