diff --git a/library/lambda.pl b/library/lambda.pl new file mode 100644 index 000000000..48da88f2a --- /dev/null +++ b/library/lambda.pl @@ -0,0 +1,204 @@ +/* + Author: Ulrich Neumerkel + E-mail: ulrich@complang.tuwien.ac.at + Copyright (C): 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. + + + +*/ + +:- module(lambda, [ + (^)/3, (^)/4, (^)/5, (^)/6, (^)/7, (^)/8, (^)/9, + (\)/1, (\)/2, (\)/3, (\)/4, (\)/5, (\)/6, (\)/7, + (+\)/2, (+\)/3, (+\)/4, (+\)/5, (+\)/6, (+\)/7, + 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 + +@tbd Static expansion similar to apply_macros. +@author Ulrich Neumerkel +*/ + +:- meta_predicate no_hat_call(0). + +:- meta_predicate + ^(?,0,?), + ^(?,1,?,?), + ^(?,2,?,?,?), + ^(?,3,?,?,?,?), + ^(?,4,?,?,?,?,?). + +^(V1,Goal,V1) :- + no_hat_call(Goal). +^(V1,Goal,V1,V2) :- + call(Goal,V2). +^(V1,Goal,V1,V2,V3) :- + call(Goal,V2,V3). +^(V1,Goal,V1,V2,V3,V4) :- + call(Goal,V2,V3,V4). +^(V1,Goal,V1,V2,V3,V4,V5) :- + call(Goal,V2,V3,V4,V5). +^(V1,Goal,V1,V2,V3,V4,V5,V6) :- + call(Goal,V2,V3,V4,V5,V6). +^(V1,Goal,V1,V2,V3,V4,V5,V6,V7) :- + call(Goal,V2,V3,V4,V5,V6,V7). + +:- meta_predicate + \(0), + \(1,?), + \(2,?,?), + \(3,?,?,?), + \(4,?,?,?,?), + \(5,?,?,?,?,?), + \(6,?,?,?,?,?,?). + +\(FC) :- + copy_term_nat(FC,C),no_hat_call(C). +\(FC,V1) :- + copy_term_nat(FC,C),call(C,V1). +\(FC,V1,V2) :- + copy_term_nat(FC,C),call(C,V1,V2). +\(FC,V1,V2,V3) :- + copy_term_nat(FC,C),call(C,V1,V2,V3). +\(FC,V1,V2,V3,V4) :- + copy_term_nat(FC,C),call(C,V1,V2,V3,V4). +\(FC,V1,V2,V3,V4,V5) :- + copy_term_nat(FC,C),call(C,V1,V2,V3,V4,V5). +\(FC,V1,V2,V3,V4,V5,V6) :- + copy_term_nat(FC,C),call(C,V1,V2,V3,V4,V5,V6). + +:- meta_predicate + +\(?,0), + +\(?,1,?), + +\(?,2,?,?), + +\(?,3,?,?,?), + +\(?,4,?,?,?,?), + +\(?,5,?,?,?,?,?), + +\(?,6,?,?,?,?,?,?). + ++\(GV,FC) :- + copy_term_nat(GV+FC,GV+C),no_hat_call(C). ++\(GV,FC,V1) :- + copy_term_nat(GV+FC,GV+C),call(C,V1). ++\(GV,FC,V1,V2) :- + copy_term_nat(GV+FC,GV+C),call(C,V1,V2). ++\(GV,FC,V1,V2,V3) :- + copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3). ++\(GV,FC,V1,V2,V3,V4) :- + copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4). ++\(GV,FC,V1,V2,V3,V4,V5) :- + copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4,V5). ++\(GV,FC,V1,V2,V3,V4,V5,V6) :- + copy_term_nat(GV+FC,GV+C),call(C,V1,V2,V3,V4,V5,V6). + + +%% no_hat_call(:Goal) +% +% Like call, but issues an error for a goal (^)/2. Such goals are +% likely the result of an insufficient number of arguments. + +no_hat_call(MGoal) :- + strip_module(MGoal, _, Goal), + ( nonvar(Goal), + Goal = (_^_) + -> throw(error(existence_error(lambda_parameters,Goal),_)) + ; call(MGoal) + ). + +% I would like to replace this by: +% V1^Goal :- throw(error(existence_error(lambda_parameters,V1^Goal),_)).