Henning Thielemann wrote:
To give a precise example: If I have a sequence of 'map's map f0 . map f1 . ... . map fn then there is some length where this is no longer collapsed to a single 'map'?
No. After applying a rule, the simplifier optimises the result of the rewriting. This means that with (map f (map g x) = map (f . g) x), map f (map g (map h xs)) is first rewritten to map (f . g) (map h xs) and the immediately to map (f . g . h) xs Rewriting does not shift the "focus" of the simplifier.
project . project . foo with the rules project (project x) = project x project (foo x) = projectFoo x
Both rules can be applied to the expression, but you get one fusion more, if you use the first one first. Let me guess, in order to solve that, I should restrict the first rule to an earlier phase than the second rule.
That's one possibility. It would be vastly preferable, however, to add the rule project (projectFoo x) = projectFoo x In general, you want your rewrite system to be confluent. I suspect that non-confluence always indicates a design problem. This is within one set of rules, of course - explicitly staged things like "rewriting back" of stuff which didn't fuse are different. Roman