Partial function application: Difference between revisions

There is no partial in Erlang, so in LFE we use a closure.

Here is the code, made more general to account for different arrities (note that to copy and paste into the LFE REPL, you'll need to leave out the docstring):

(defun partial

"The partial function is arity 2 where the first parameter must be a

function and the second parameter may either be a single item or a list of

items.

When funcall is called against the result of the partial call, a second

parameter is applied to the partial function. This parameter too may be

either a single item or a list of items."

((func args-1) (when (is_list args-1))

(match-lambda

((args-2) (when (is_list args-2))

(apply func (++ args-1 args-2)))

((arg-2)

(apply func (++ args-1 `(,arg-2))))))

((func arg-1)

(match-lambda

((args-2) (when (is_list args-2))

(apply func (++ `(,arg-1) args-2)))

((arg-2)

(funcall func arg-1 arg-2)))))

</lang>

Here is the problem set:

<lang lisp>

(defun fs (f s) (lists:map f s))

(defun f1 (i) (* i 2))

(defun f2 (i) (math:pow i 2))

(set fsf1 (partial #'fs/2 #'f1/1))

(set fsf2 (partial #'fs/2 #'f2/1))

(set seq1 '((0 1 2 3)))

(set seq2 '((2 4 6 8)))

> (funcall fsf1 seq1)

(0 2 4 6)

> (funcall fsf2 seq1)

(0.0 1.0 4.0 9.0)

> (funcall fsf1 seq2)

(4 8 12 16)

> (funcall fsf2 seq2)

(4.0 16.0 36.0 64.0)