GHC rewrite rules and constructor wrappers?

Conal Elliott conal at
Tue Apr 29 22:02:53 UTC 2014

I'm trying to sort out the relationship of GHC rewrite rules and
constructor wrappers. I have rules like

> "reify/(:<)" reifyEP (:<) = kPrim VecSP

This rule seems to fire for `reifyEP ($W:<)` rather than `reifyEP (:<)`. If
I'm tracking (uncertain), `($W:<)` inlines to `(:<)`. Sometimes I'm able to
preserve the `$W` form, but sometimes I get the bare form when inlining a
definition from another already-compiled module. In those cases, I don't
know how to get my rules to fire.

Advice and explanation appreciated, including pointers explanations of the
role of these wrappers in GHC.

-- Conal
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