Brandon Allbery wrote
No. The point is, it's not simply a type annotation; it's a *value* (a dictionary) that must be carried along with the rest of the value somehow. The compiler can't always work out statically which instances need to be used with the affected value, so it has to be available at run time; the context is effectively declaring that the run-time dictionary is a required extra parameter. And it wouldn't really be workable for some types to secretly imply that extra parameter and others not.
Why not let all types carry the dictionary automatically, or at least every time that it's used, if that would incur a memory/performance penalty? GHC tells me which context to add when it's missing, so it clearly knows. -- View this message in context: http://haskell.1045720.n5.nabble.com/How-to-fix-DatatypeContexts-tp5733103p5... Sent from the Haskell - Glasgow-haskell-users mailing list archive at Nabble.com.