Haskell Language Overloaded Literals
Remarks
Integer Literals
is a numeral without a decimal point
for example 0, 1, 42, ...
is implicitly applied to fromInteger which is part of the Num type class so it indeed has type Num a => a - that is it can have any type that is an instance of Num
Fractional Literals
is a numeral with a decimal point
for example 0.0, -0.1111, ...
is implicitly applied to fromRational which is part of the Fractional type class so it indeed has type a => a - that is it can have any type that is an instance of Fractional
String Literals
If you add the language extension OverloadedStrings to GHC you can have the same for String-literals which then are applied to fromString from the Data.String.IsString type class
This is often used to replace String with Text or ByteString.
List Literals
Lists can defined with the [1, 2, 3] literal syntax. In GHC 7.8 and beyond, this can also be used to define other list-like structures with the OverloadedLists extension.
By default, the type of [] is:
> :t []
[] :: [t]
With OverloadedLists, this becomes:
[] :: GHC.Exts.IsList l => l
