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Function composition: Difference between revisions
Emacs Lisp: Replace obsolete code with lexical binding example
(Added Mathcad example.) |
(Emacs Lisp: Replace obsolete code with lexical binding example) |
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=={{header|Emacs Lisp}}==
A <code>lambda</code> form can be constructed with the desired <code>f</code> and <code>g</code> inserted. The result is simply a list. A list starting with <code>lambda</code> is a function.▼
Lexical binding is supported as of Emacs 24.1, allowing the use of a closure for function composition.
<lang Lisp>;; lexical-binding: t
(defun compose (f g)▼
(let ((func (compose '1+ '1+)))▼
(funcall func 5)) ;=> 7</lang>▼
▲
<lang Lisp>(defun compose (f g)
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(let ((func (compose '1+ '1+)))
(funcall func 5)) ;=> 7</lang>
A similar thing can be done with a macro like the following. It differs in that the arguments should be unquoted symbols, and if they're expressions then they're evaluated on every call to the resulting <code>lambda</code>.
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(let ((func (compose 1+ 1+)))
(funcall func 5)) ;=> 7</lang>
▲(defun compose (f g)
▲ (lambda (x)
▲ (funcall f (funcall g x)))))
▲(let ((func (compose '1+ '1+)))
▲ (funcall func 5))
=={{header|Erlang}}==
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