1/* 2 Author: Ulrich Neumerkel 3 E-mail: ulrich@complang.tuwien.ac.at 4 Copyright (C): 2009 Ulrich Neumerkel. All rights reserved. 5 6Redistribution and use in source and binary forms, with or without 7modification, are permitted provided that the following conditions are 8met: 9 101. Redistributions of source code must retain the above copyright 11 notice, this list of conditions and the following disclaimer. 12 132. Redistributions in binary form must reproduce the above copyright 14 notice, this list of conditions and the following disclaimer in the 15 documentation and/or other materials provided with the distribution. 16 17THIS SOFTWARE IS PROVIDED BY Ulrich Neumerkel ``AS IS'' AND ANY 18EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 20PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL Ulrich Neumerkel OR 21CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 22EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 23PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 24PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 25LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 26NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 27SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 29The views and conclusions contained in the software and documentation 30are those of the authors and should not be interpreted as representing 31official policies, either expressed or implied, of Ulrich Neumerkel. 32 33 34 35*/ 36 37:- module(lambda, [ 38 (^)/3, (^)/4, (^)/5, (^)/6, (^)/7, (^)/8, (^)/9, 39 (\)/1, (\)/2, (\)/3, (\)/4, (\)/5, (\)/6, (\)/7, 40 (+\)/2, (+\)/3, (+\)/4, (+\)/5, (+\)/6, (+\)/7, 41 op(201,xfx,+\)]).

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

author: - Ulrich Neumerkel */
To be done: - Static expansion similar to apply_macros.

117:- meta_predicate no_hat_call(0). 118 119:- meta_predicate 120 ^(?,0,?), 121 ^(?,1,?,?), 122 ^(?,2,?,?,?), 123 ^(?,3,?,?,?,?), 124 ^(?,4,?,?,?,?,?), 125 ^(?,5,?,?,?,?,?,?), 126 ^(?,6,?,?,?,?,?,?,?). 127 128 129 130^(V1,Goal,V1) :- 131 no_hat_call(Goal). 132^(V1,Goal,V1,V2) :- 133 call(Goal,V2). 134^(V1,Goal,V1,V2,V3) :- 135 call(Goal,V2,V3). 136^(V1,Goal,V1,V2,V3,V4) :- 137 call(Goal,V2,V3,V4). 138^(V1,Goal,V1,V2,V3,V4,V5) :- 139 call(Goal,V2,V3,V4,V5). 140^(V1,Goal,V1,V2,V3,V4,V5,V6) :- 141 call(Goal,V2,V3,V4,V5,V6). 142^(V1,Goal,V1,V2,V3,V4,V5,V6,V7) :- 143 call(Goal,V2,V3,V4,V5,V6,V7). 144 145:- meta_predicate 146 \(0), 147 \(1,?), 148 \(2,?,?), 149 \(3,?,?,?), 150 \(4,?,?,?,?), 151 \(5,?,?,?,?,?), 152 \(6,?,?,?,?,?,?). 153 154\(FC) :- 155 copy_term_nat(FC,C),no_hat_call(C). 156\(FC,V1) :- 157 copy_term_nat(FC,C),call(C,V1). 158\(FC,V1,V2) :- 159 copy_term_nat(FC,C),call(C,V1,V2). 160\(FC,V1,V2,V3) :- 161 copy_term_nat(FC,C),call(C,V1,V2,V3). 162\(FC,V1,V2,V3,V4) :- 163 copy_term_nat(FC,C),call(C,V1,V2,V3,V4). 164\(FC,V1,V2,V3,V4,V5) :- 165 copy_term_nat(FC,C),call(C,V1,V2,V3,V4,V5). 166\(FC,V1,V2,V3,V4,V5,V6) :- 167 copy_term_nat(FC,C),call(C,V1,V2,V3,V4,V5,V6). 168 169:- meta_predicate 170 +\(?,0), 171 +\(?,1,?), 172 +\(?,2,?,?), 173 +\(?,3,?,?,?), 174 +\(?,4,?,?,?,?), 175 +\(?,5,?,?,?,?,?), 176 +\(?,6,?,?,?,?,?,?). 177 178+\(GV,FC) :- 179 copy_term_nat(GV+FC,GV+C),no_hat_call(C). 180+\(GV,FC,V1) :- 181 copy_term_nat(GV+FC,GV+C),call(C,V1). 182+\(GV,FC,V1,V2) :- 183 copy_term_nat(GV+FC,GV+C),call(C,V1,V2). 184+\(GV,FC,V1,V2,V3) :- 185 copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3). 186+\(GV,FC,V1,V2,V3,V4) :- 187 copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4). 188+\(GV,FC,V1,V2,V3,V4,V5) :- 189 copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4,V5). 190+\(GV,FC,V1,V2,V3,V4,V5,V6) :- 191 copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4,V5,V6).

199no_hat_call(MGoal) :- 200 strip_module(MGoal, _, Goal), 201 ( nonvar(Goal), 202 Goal = (_^_) 203 -> throw(error(existence_error(lambda_parameters,Goal),_)) 204 ; call(MGoal) 205 ). 206 207% I would like to replace this by: 208% V1^Goal :- throw(error(existence_error(lambda_parameters,V1^Goal),_)).