library(lambda)

Description

/**  Lambda expressions

This library provides lambda expressions to simplify higher order
programming based on call/N.

Lambda expressions are represented by ordinary Prolog terms.
There are two kinds of lambda expressions:

    Free+\X1^X2^ ..^XN^Goal

         \X1^X2^ ..^XN^Goal

The second is a shorthand for t+\X1^X2^..^XN^Goal.

Xi are the parameters.

Goal is a goal or continuation. Syntax note: Operators within Goal
require parentheses due to the low precedence of the ^ operator.

Free contains variables that are valid outside the scope of the lambda
expression. They are thus free variables within.

All other variables of Goal are considered local variables. They must
not appear outside the lambda expression. This restriction is
currently not checked. Violations may lead to unexpected bindings.

In the following example the parentheses around X>3 are necessary.

==
?- use_module(library(lambda)).
?- use_module(library(apply)).

?- maplist(\X^(X>3),[4,5,9]).
true.
==

In the following X is a variable that is shared by both instances of
the lambda expression. The second query illustrates the cooperation of
continuations and lambdas. The lambda expression is in this case a
continuation expecting a further argument.

==
?- Xs = [A,B], maplist(X+\Y^dif(X,Y), Xs).
Xs = [A, B],
dif(X, A),
dif(X, B).

?- Xs = [A,B], maplist(X+\dif(X), Xs).
Xs = [A, B],
dif(X, A),
dif(X, B).
==

The following queries are all equivalent. To see this, use
the fact f(x,y).
==
?- call(f,A1,A2).
?- call(\X^f(X),A1,A2).
?- call(\X^Y^f(X,Y), A1,A2).
?- call(\X^(X+\Y^f(X,Y)), A1,A2).
?- call(call(f, A1),A2).
?- call(f(A1),A2).
?- f(A1,A2).
A1 = x,
A2 = y.
==

Further discussions
http://www.complang.tuwien.ac.at/ulrich/Prolog-inedit/ISO-Hiord

@tbd Static expansion similar to apply_macros.
@author Ulrich Neumerkel
*/

About

• Author: Ulrich Neumerkel, ulrich@complang.tuwien.ac.at (ECLiPSe port: Joachim Schimpf)
• Copyright © 2009 Ulrich Neumerkel. All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY Ulrich Neumerkel ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Ulrich Neumerkel OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. The views and conclusions contained in the software and documentation are those of the authors and should not be interpreted as representing official policies, either expressed or implied, of Ulrich Neumerkel.