That workaround is fragile for me:

When I put everything into one file, the "fromList/toList" rule fires.

However, when I put the test1 and main definitions into a separate file, the "fromList/toList" rule no longer fires.

The reason for that seems to be that " fromList' = fromList " is rewritten to " fromList' = fromList' ", and then the strictness/demand analysis flags it up as always bottoming.

Then in the file where we write `test1 x = fromList (toList x)`, it gets rewritten to `test1 x = fromList' (toList x)`, after which (because of the always bottoming) it gets rewritten to `test1 _ = case fromList' of {}`

On Sat, 7 Mar 2020 at 02:56, Dr. ÉRDI Gergő <gergo@erdi.hu> wrote:

As a workaround, can you try this? https://stackoverflow.com/a/32133083/477476

On Fri, Mar 6, 2020, 23:23 Christiaan Baaij <christiaan.baaij@gmail.com> wrote:
Hello,

The other day I was experimenting with RULES and got this warning:

src/Clash/Sized/Vector.hs:2159:11: warning: [-Winline-rule-shadowing]
Rule "map Pack" may never fire
because rule "Class op pack" for ‘pack’ might fire first
Probable fix: add phase [n] or [~n] to the competing rule
|
2159 | {-# RULES "map Pack" map pack = id #-}

The warning seems to suggests two things:
1. "Class op" -> "dictionary projection" are implemented as rewrite rules and executed the same way as other user-defined RULES
2. These rules run first, and you cannot run anything before them

Now my question is, is 1. actually true? or is that warning just a (white) lie?
If 1. is actually true, would there be any objections to adding a "-1" phase: where RULES specified to start from phase "-1" onward fire before any of the Class op rules.
I'm quite willing to implement the above if A) Class op rules are actually implemented as builtin RULES; B) there a no objections to this "-1" phase.

Thanks,
Christiaan

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