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# LANGUAGE pragma Haskell extensions
List: https://downloads.haskell.org/~ghc/7.0.3/docs/html/libraries/Cabal-1.10.1.0/Language-Haskell-Extension.html
## Using
Put as *first* line of file:
{-# LANGUAGE Extension, ... -#}
## FlexibleContexts
Relax some restrictions on the form of the context of a type signature.
Normally typeclass constraints have to have type variable arguments.
modify :: MonadState s m => (s -> s) -> m ()
With FlexibleContexts, can be any type (?)
modifyFst :: MonadState (a, b) m => (a -> a) -> m ()
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