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Simon Peyton Jones authored
The loop-breaking heuristics were making it a high priority to avoid choosing a variable as a loop breaker if its *type* was a data type. The reason is that it's very good to be able to "see" constructor applications. But it's only good if the constructor application is *visible*, so that is what I test for now. I found a case (when testing SpecConstr) where I had a Rec like this: rec { lvl = foo Nothing foo = ... RULE foo Nothing = ... } Even if lvl has a data type, it's much better to make lvl the loop breaker, not foo, so that foo's RULE is visible in lvl's RHS.
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