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Simon Peyton Jones authored
The IdBindingInfo field of ATcId serves two purposes - to control generalisation when we have -XMonoLocalBinds - to check for floatability when dealing with (static e) These are related, but not the same, and they'd becomme confused. Trac #13804 showed this up via an example like this: f periph = let sr :: forall a. [a] -> [a] sr = if periph then reverse else id sr2 = sr -- The question: is sr2 generalised? -- It should be, because sr has a type sig -- even though it has periph free in (sr2 [True], sr2 "c") Here sr2 should be generalised, despite the free var 'periph' in 'sr' because 'sr' has a closed type signature. I documented all this very carefully this time, in TcRnTypes: Note [Meaning of IdBindingInfo] Note [Bindings with closed types: ClosedTypeId]
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