(lispkit combinator)
Library
(lispkit combinator) defines abstractions for combinator-style programming. It provides means to create and compose functions.
(const c ...) 
Returns a function accepting any number of arguments and returning the values
c ... .(flip f)
Takes a function with two parameters and returns an equivalent function where the two parameters are swapped.
(define snoc (flip cons))
(snoc (snoc (snoc '() 3) 2) 1) ⟹ (1 2 3)
(negate f)
Returns a function which invokes
f and returns the logical negation.(define gvector-has-elements? (negate gvector-empty?))
(gvector-has-elements? #g(1 2 3)) ⟹ #t
(partial f arg ...)
Applies arguments arg ... partially to f and returns a new function accepting the remaining arguments. For a function
(f a1 a2 a3 ... an), (partial f a1 a2) will return a function (lambda (a3 ... an) (f a1 a2 a3 ... an)).(compose f ...)
Composes the given functions f ... such that
((compose f1 f2 ... fn) x) is equivalent to (f1 (f2 (... (fn x)))). compose supports functions returning multiple arguments.(o f ...)
Composes the given functions f ... such that
((o f1 f2 ... fn) x) is equivalent to (f1 (f2 (... (fn x)))). o is a more efficient version of compose which only works if the involved functions only return a single argument. compose is more general and supports functions returning multiple arguments.(conjoin f ...)
Returns a function invoking all functions f ... and combining the results with
and. ((conjoin f1 f2 ...) x ...) is equivalent to (and (f1 x ...) (f2 x ...) ...).(disjoin f ...)
Returns a function invoking all functions f ... and combining the results with
or. ((disjoin f1 f2 ...) x ...) is equivalent to (or (f1 x ...) (f2 x ...) ...).(list-of? f)
Returns a predicate which takes a list as its argument and returns
#t if for every element x of the list (f x) returns true.(each f ...)
Returns a function which applies the functions
f ... each individually to its arguments in the given order, returning the result of the last function application.(cut f) 
(cut f <...>)
(cut f arg ...)
(cut f arg ... <...>)
Special form
cut transforms an expression (f arg ...) into a lambda expression with as many formal variables as there are slots <> in the expression (f arg ...). The body of the resulting lambda expression calls procedure f with arguments arg ... in the order they appear. In case there is a rest symbol <...> at the end, the resulting procedure is of variable arity, and the body calls f with all arguments provided to the actual call of the specialized procedure.(cut cons (+ a 1) <>) ⟹ (lambda (x2) (cons (+ a 1) x2))
(cut list 1 <> 3 <> 5) ⟹ (lambda (x2 x4) (list 1 x2 3 x4 5))
(cut list 1 <> 3 <...>) ⟹ (lambda (x2 . xs) (apply list 1 x2 3 xs))
(cute f)
(cute f <...>)
(cute f arg ...)
(cute f arg ... <...>)
Special form
cute is similar to cut, except that it first binds new variables to the result of evaluating the non-slot expressions (in an unspecific order) and then substituting the variables for the non-slot expressions. In effect, cut evaluates non-slot expressions at the time the resulting procedure is called, whereas cute evaluates the non-slot expressions at the time the procedure is constructed.(cute cons (+ a 1) <>)
⟹ (let ((a1 (+ a 1))) (lambda (x2) (cons a1 x2)))
(Y f)
Y combinator for computing a fixed point of a function f. This is a value that is mapped to itself.
; factorial function
(define fac
(Y (lambda (r)
(lambda (x) (if (< x 2) 1 (* x (r (- x 1))))))))
; fibonacci numbers
(define fib
(Y (lambda (f)
(lambda (x)
(if (< x 2) x (+ (f (- x 1)) (f (- x 2))))))))
Last modified 5mo ago