Talk:Y combinator: Difference between revisions
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:: Understood – many thanks for the explanations – will you fix the non-compiling part and revert the rest in the way seems best to you ? [[User:Hout|Hout]] ([[User talk:Hout|talk]]) 22:31, 10 October 2018 (UTC)
::: Good edits and explanations. Many thanks. [[User:Hout|Hout]] ([[User talk:Hout|talk]]) 11:53, 11 October 2018 (UTC)
::::Done and dusted...
::::While I was making sure everything compiled, I did some performance tests, with some interesting results...
::::I didn't change the first and second parts much other than to make the code producing lazy lists functions so the lists can be consumed as evaluated as discussed above, and forced evaluations so they wouldn't be deferred until the end of the calculation, which need showed up in performance testing.
::::However, performance and capability as far as range of usefulness stunk, so I added back the working simple function recursive versions, which are at least ten times faster, don't take so much memory, don't crash for large ranges, and which compile easily without showing up compiler bugs. I'm a little harsh in evaluating the usefulness of the Y-combinator unless someone can show the error in my analysis...
::::As always, I monitor this Talk page and the main page if anyone would like to discuss it...--[[User:GordonBGood|GordonBGood]] ([[User talk:GordonBGood|talk]]) 12:05, 11 October 2018 (UTC)
:::::I've been asked to remove the non-Y-combinator versions as off the topic of this task and am in process of doing so. I believe the task should be modified in two ways: 1) to clarify if function recursion is allowed although binding recursion clearly isn't: if function recursion isn't allowed then the second Haskell example wouldn't be allowed either, and 2) it should be noted that, other than as an interesting intellectual exercise, the Y-combinator/Z-combinator is rarely of practical use other than for implementing recursion for languages that don't support it, as for languages that do support recursion (the majority of modern languages at least support function recursion) its use comes at a sometimes major performance cost.--[[User:GordonBGood|GordonBGood]] ([[User talk:GordonBGood|talk]]) 01:47, 13 October 2018 (UTC)
==Problem with the first non function recursive Haskell version of Y-combinator==
The first non function recursive implementation of the Y-combinator <code>fix</code> doesn't compile using either GHC version 8.4.3 or 8.6.1 on 64-bit Windows other than in non-optimized interpretive mode (-O0), with an error message about exceeding the "tick count", but increasing this "tick count" immensely doesn't help. Error message as follows:
<pre>Simplifier ticks exhausted
When trying UnfoldingDone x_s3FU
To increase the limit, use -fsimpl-tick-factor=N (default 100).
If you need to increase the limit substantially, please file a
bug report and indicate the factor you needed.
If GHC was unable to complete compilation even with a very large factor
(a thousand or more), please consult the "Known bugs or infelicities"
section in the Users Guide before filing a report. There are a
few situations unlikely to occur in practical programs for which
simplifier non-termination has been judged acceptable.
To see detailed counts use -ddump-simpl-stats
Total ticks: 11445</pre>
Someone more knowledgeable than I should investigate whether it is possible to modify this to fully compile with optimizations. With optimization, the only versions of the Y-combinator usable on current GHC versions are the built-in one using binding recursion or the second version using function recursion posted here--[[User:GordonBGood|GordonBGood]] ([[User talk:GordonBGood|talk]]) 01:47, 13 October 2018 (UTC)
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