9.2 Functions and Types
TBoS p 192 onwards
Shen is an explicitly typed polymorphic language in the manner of Hope; it requires that functions be entered with their types.
A --> B --> C is shorthand for A --> (B --> C). Signatures are entered in }...{ immediately after the name of the function.
(define member
}A --> (list A) --> boolean{
_ [] -> false
X [X | _] -> true
X [_ | Y] -> (member X Y))
member : (A --> ((list A) --> boolean))
(define square
}number --> number{
X -> (* X X))
square : (number --> number)
(define swap
}(A * B) --> (B * A){
(@p X Y) -> (@p Y X))
swap : ((A * B) --> (B * A))
(define unit-vector?
}(vector A) --> boolean{
(@v _ <>) -> true
_ -> false)
unit-vector? : ((vector A) --> boolean)
(define unit-string?
}string --> boolean{
(@s _ "") -> true
_ -> false)
unit-string? : (string --> boolean)
(member 1 [1 2 3])
true : boolean
(square 4)
16 : number
(swap (@p 1 2))
(@p 2 1) : (number * number)
(unit-vector? (@v 1 <>))
true : boolean
(unit-string? "a")
true : boolean
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