module Syntax.Basic.SpecialCompilerFeatures.TypedWildcards where
Sometimes, when writing code, we're not always sure what type something
should be in a type signature.
In such cases, we can use a feature called "typed wildcards"
to ask the compiler to tell us which type it thinks should go there.
This feature can often be very helpful when debugging a compiler error
or when exploring a new library for the first time.
Typed Wildcards can be either unnamed ("_") or named "?name".
Named typed wildcards will emit a compiler error whereas
unnamed typed wildcards will emit a compiler warning.
someValue :: _ -- unnamed typed wildcard
The '_' character above is an unnamed typed wildcard
It will produce a compiler warning whose message will include
the compiler's guess as to what goes there.
-- Uncomment the below code and then rebuild the folder to see what happens
-- someValue2 :: ?TellMeTheType
-- someValue2 =
-- The "?name" syntax above is a named typed wildcard.
-- It will produce a compiler error whose message will include
-- the compiler's guess as to which type goes there.