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=== Assigning functions to variables ===
[[Assignment (computer science)|Assigning]] functions to [[variable (computer science)|variables]] and storing them inside (global)
<syntaxhighlight lang="haskell">
f :: [[Integer] -> [Integer]]
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; [[Intensional equality]]: Under intensional equality, two functions ''f'' and ''g'' are considered equal if they have the same "internal structure". This kind of equality could be implemented in [[interpreted language]]s by comparing the [[source code]] of the function bodies (such as in Interpreted Lisp 1.5) or the [[object code]] in [[compiled language]]s. Intensional equality implies extensional equality (assuming the functions are deterministic and have no hidden inputs, such as the [[program counter]] or a mutable [[global variable]].)
; [[Reference equality]]: Given the impracticality of implementing extensional and intensional equality, most languages supporting testing functions for equality use reference equality. All functions or closures are assigned a unique identifier (usually the address of the function body or the closure) and equality is decided based on equality of the identifier. Two separately defined, but otherwise identical function definitions will be considered unequal. Referential equality implies intensional and extensional equality. Referential equality breaks [[referential transparency]] and is therefore not supported in [[
== Type theory ==
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