#9183: GHC shouldn't expand constraint synonyms -------------------------------------+------------------------------------ Reporter: Feuerbach | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by simonpj): I see what you want, but I don't see how to achieve it. Recall that * `:info f` takes a name `f` and tells you stuff about `f` * `:type e` takes an abritrary expression `e` and tells you its type If you use `:info showX` you'll see the type you expect. If you use `:type showX` you are using `:type` with an "arbitrary expression" that turns out to be a single identifier. So GHC instantiates it with fresh type variables, generates constraints, simplifies them, and then re- generalises. The instantiation, constraint simplification, and regeneration is what expands the constraint synonym, and I don't see a robust way to stop that happening. We could make `:type` behave like `:info` when given a bare identifier. Or, in those same circumstances, we would make `:type` refrain from the "instantiate, simplify, generalise" hoopla. But that would make `:type` on a bare identifier behave subtly differently to the way it does now.Is that special case worth it? Or would it be better to encourage users to use `:info` whenever possible? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9183#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler