Pedro Vasconcelos wrote:
This is because all input and output data flow is type checked in a
function application, whereas imperative side effects might escape
checking.
For example, the type signature for a variable swapping procedure in C:
void swap(int *a, int *b)
This will still type check even if it modified only one of the argument
references. However, if written functionally, it must return a pair:
swap :: (Int,Int) -> (Int,Int)
This benefit of explicit input and output values can interact nicely
with parametric polymorphism:
swap :: (a, b) -> (b, a)
This more general type signature makes sure we are not just returning
the input values unswapped.
Tillmann
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