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Other than loading a Haskell file into GHCi and then using :type <expr>, is there any way to have the compiler display types for all of the functions as they are compiled?
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Functions can also be passed as arguments or returned (as we have seen). Their types are given in the type signature. *Main> :t map map :: (a -> b) -> [a] -> [b] *Main> :t filter filter :: (a -> Bool) -> [a] -> [a] flip_args :: (a -> b -> c) -> b -> a -> c flip_args f x y = f y x.
a. to just print it during compilation, you could enable PartialSignatures extension, and add to arbitrary expression signature :: _ , then its type will be printed during compilation. b. to actually get the type as a data for runtime handling, you could use TemplateHaskell extension and function reify from it.
If you need to figure out what the type of an object is in a Haskell program, I hope this is helpful. Note that if you are in GHCI, you can just put :type before your expression to determine the expression's type, or use :set +t to see the type of every expression in GHCI.
The shows functions return a function that prepends the output String to an existing String . This allows constant-time concatenation of results using function composition.
If you pass -fwarn-missing-signatures (or -Wall) to GHC it will list every top-level function that has no type annotation in the file, together with the inferred type.
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