RULES that never fire (automatically)

We want a way of having GHC RULES known by GHC, but not used by the optimizer.

HERMIT, a interactive plugin for GHC that applies rules - and as well as built in rules (like alpha conversion, beta-reduction, etc) - also provide access to the named GHC RULES. Here is the rub: We want to use GHC RULES that are parsed and typed checked like normal rules, are visible to the HERMIT system, but never run by the simplifier. Currently we can say

• attempt this before this (opt) pass, or
• attempt after this pass, but there is no way of saying
• never attempt.

We were thinking

    {-# RULES [~] "map/map" forall f g . map f (map g xs) = map (f.g) xs #-}

Where the [~] says *never* execute this without be explicitly asked, following on from the [~0] which does not run in first pass.

We are happy making the required changes.