Thank you for raising this issue, Christiaan! The current policy (very early class-op inlining) is a major difficulty and the main source of fragility in my compiling-to-categories implementation. I have a tediously programmed and delicately balanced collection of techniques to intercept and transform class ops to non-ops early and then transform back late for elimination, but it doesn't work in all situations. Since class operations roughly correspond to operations in various algebraic abstractions---interfaces with laws---I often want to exploit exactly those laws as rewrite rules, and yet those rules currently cannot be used dependably. - Conal

On Fri, Mar 6, 2020 at 7:22 AM 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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