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    1/*  Part of SWI-Prolog
    2
    3    Author:        Paulo Moura
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2015, Paulo Moura, Kyndi Inc., VU University Amsterdam
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(yall,
   36          [ (>>)/2, (>>)/3, (>>)/4, (>>)/5, (>>)/6, (>>)/7, (>>)/8, (>>)/9,
   37            (/)/2, (/)/3, (/)/4, (/)/5, (/)/6, (/)/7, (/)/8, (/)/9,
   38
   39            lambda_calls/2,                     % +LambdaExt, -Goal
   40            lambda_calls/3,                     % +Lambda, +Args, -Goal
   41            is_lambda/1                         % @Term
   42          ]).   43:- use_module(library(error)).   44:- use_module(library(lists)).   45
   46:- meta_predicate
   47    '>>'(?, 0),
   48    '>>'(?, :, ?),
   49    '>>'(?, :, ?, ?),
   50    '>>'(?, :, ?, ?, ?),
   51    '>>'(?, :, ?, ?, ?, ?),
   52    '>>'(?, :, ?, ?, ?, ?, ?),
   53    '>>'(?, :, ?, ?, ?, ?, ?, ?),
   54    '>>'(?, :, ?, ?, ?, ?, ?, ?, ?).   55
   56:- meta_predicate
   57    '/'(?, 0),
   58    '/'(?, 1, ?),
   59    '/'(?, 2, ?, ?),
   60    '/'(?, 3, ?, ?, ?),
   61    '/'(?, 4, ?, ?, ?, ?),
   62    '/'(?, 5, ?, ?, ?, ?, ?),
   63    '/'(?, 6, ?, ?, ?, ?, ?, ?),
   64    '/'(?, 7, ?, ?, ?, ?, ?, ?, ?).

Lambda expressions

Prolog realizes high-order programming with meta-calling. The core predicate of this is call/1, which simply calls its argument. This can be used to define higher-order predicates such as ignore/1 or forall/2. The call/N construct calls a closure with N-1 additional arguments. This is used to define higher-order predicates such as the maplist/N family or foldl/N.

The problem with higher order predicates based on call/N is that the additional arguments are always added to the end of the closure's argument list. This often requires defining trivial helper predicates to get the argument order right. For example, if you want to add a common postfix to a list of atoms you need to apply atom_concat(In,Postfix,Out), but maplist(x(PostFix),ListIn,ListOut) calls x(PostFix,In,Out). This is where this library comes in, which allows us to write

?- maplist([In,Out]>>atom_concat(In,'_p',Out), [a,b], ListOut).
ListOut = [a_p, b_p].

The {...} specifies which variables are shared between the lambda and the context. This allows us to write the code below. Without the {PostFix} a free variable would be passed to atom_concat/3.

add_postfix(PostFix, ListIn, ListOut) :-
    maplist({PostFix}/[In,Out]>>atom_concat(In,PostFix,Out),
            ListIn, ListOut).

This introduces the second application area of lambda expressions: the ability to stop binding variables in the context. This features shines when combined with bagof/3 or setof/3 where you normally have to specify the the variables in whose binding you are not interested using the Var^Goal construct (marking Var as existential quantified). Lambdas allow doing the reverse: specify the variables in which you are interested.

Lambda expressions use the syntax below

{...}/[...]>>Goal.

The {...} optional part is used for lambda-free variables. The order of variables doesn't matter hence the {...} set notation.

The [...] optional part lists lambda parameters. Here order of variables matters hence the list notation.

As / and >> are standard infix operators, no new operators are added by this library. An advantage of this syntax is that we can simply unify a lambda expression with Free/Parameters>>Lambda to access each of its components. Spaces in the lambda expression are not a problem although the goal may need to be written between ()'s. Goals that are qualified by a module prefix also need to be wrapped inside parentheses.

Combined with library(apply_macros), library(yall) allows writing one-liners for many list operations that have the same performance as hand written code.

The module name, yall, stands for Yet Another Lambda Library.

This module implements Logtalk's lambda expressions syntax. The development of this module was sponsored by Kyndi, Inc.

author
- Paulo Moura and Jan Wielemaker */
To be done
- Extend optimization support



 +Parameters >> +Lambda


 >>(+Parameters, +Lambda, ?A1)


 >>(+Parameters, +Lambda, ?A1, ?A2)


 >>(+Parameters, +Lambda, ?A1, ?A2, ?A3)


 >>(+Parameters, +Lambda, ?A1, ?A2, ?A3, ?A4)


 >>(+Parameters, +Lambda, ?A1, ?A2, ?A3, ?A4, ?A5)


 >>(+Parameters, +Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6)


 >>(+Parameters, +Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6, ?A7)
Calls a copy of Lambda. This is similar to call(Lambda,A1,...),
but arguments are reordered according to the list Parameters:





Arguments:





Parameters- is either a plain list of parameters or a term
{Free}/List. Free represents variables that are
shared between the context and the Lambda term. This
is needed for compiling Lambda expressions.












  161'>>'(Parms, Lambda) :-
  162    unify_lambda_parameters(Parms, [],
  163                            ExtraArgs, Lambda, LambdaCopy),
  164    Goal =.. [call, LambdaCopy| ExtraArgs],
  165    call(Goal).
  166
  167'>>'(Parms, Lambda, A1) :-
  168    unify_lambda_parameters(Parms, [A1],
  169                            ExtraArgs, Lambda, LambdaCopy),
  170    Goal =.. [call, LambdaCopy| ExtraArgs],
  171    call(Goal).
  172
  173'>>'(Parms, Lambda, A1, A2) :-
  174    unify_lambda_parameters(Parms, [A1,A2],
  175                            ExtraArgs, Lambda, LambdaCopy),
  176    Goal =.. [call, LambdaCopy| ExtraArgs],
  177    call(Goal).
  178
  179'>>'(Parms, Lambda, A1, A2, A3) :-
  180    unify_lambda_parameters(Parms, [A1,A2,A3],
  181                            ExtraArgs, Lambda, LambdaCopy),
  182    Goal =.. [call, LambdaCopy| ExtraArgs],
  183    call(Goal).
  184
  185'>>'(Parms, Lambda, A1, A2, A3, A4) :-
  186    unify_lambda_parameters(Parms, [A1,A2,A3,A4],
  187                            ExtraArgs, Lambda, LambdaCopy),
  188    Goal =.. [call, LambdaCopy| ExtraArgs],
  189    call(Goal).
  190
  191'>>'(Parms, Lambda, A1, A2, A3, A4, A5) :-
  192    unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5],
  193                            ExtraArgs, Lambda, LambdaCopy),
  194    Goal =.. [call, LambdaCopy| ExtraArgs],
  195    call(Goal).
  196
  197'>>'(Parms, Lambda, A1, A2, A3, A4, A5, A6) :-
  198    unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5,A6],
  199                            ExtraArgs, Lambda, LambdaCopy),
  200    Goal =.. [call, LambdaCopy| ExtraArgs],
  201    call(Goal).
  202
  203'>>'(Parms, Lambda, A1, A2, A3, A4, A5, A6, A7) :-
  204    unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5,A6,A7],
  205                            ExtraArgs, Lambda, LambdaCopy),
  206    Goal =.. [call, LambdaCopy| ExtraArgs],
  207    call(Goal).



 +Free / :Lambda


 /(+Free, :Lambda, ?A1)


 /(+Free, :Lambda, ?A1, ?A2)


 /(+Free, :Lambda, ?A1, ?A2, ?A3)


 /(+Free, :Lambda, ?A1, ?A2, ?A3, ?A4)


 /(+Free, :Lambda, ?A1, ?A2, ?A3, ?A4, ?A5)


 /(+Free, :Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6)


 /(+Free, :Lambda, ?A1, ?A2, ?A3, ?A4, ?A5, ?A6, ?A7)
Shorthand for Free/[]>>Lambda. This is the same as applying
call/N on Lambda, except that only variables appearing in Free
are bound by the call. For example


p(1,a).
p(2,b).

?- {X}/p(X,Y).
X = 1;
X = 2.




This can in particularly be combined with bagof/3 and setof/3 to
select particular variables to be concerned rather than using
existential quantification (^/2) to exclude variables. For
example, the two calls below are equivalent.



setof(X, Y^p(X,Y), Xs)
setof(X, {X}/p(X,_), Xs)





  242'/'(Free, Lambda) :-
  243    lambda_free(Free),
  244    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  245    call(LambdaCopy).
  246
  247'/'(Free, Lambda, A1) :-
  248    lambda_free(Free),
  249    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  250    call(LambdaCopy, A1).
  251
  252'/'(Free, Lambda, A1, A2) :-
  253    lambda_free(Free),
  254    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  255    call(LambdaCopy, A1, A2).
  256
  257'/'(Free, Lambda, A1, A2, A3) :-
  258    lambda_free(Free),
  259    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  260    call(LambdaCopy, A1, A2, A3).
  261
  262'/'(Free, Lambda, A1, A2, A3, A4) :-
  263    lambda_free(Free),
  264    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  265    call(LambdaCopy, A1, A2, A3, A4).
  266
  267'/'(Free, Lambda, A1, A2, A3, A4, A5) :-
  268    lambda_free(Free),
  269    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  270    call(LambdaCopy, A1, A2, A3, A4, A5).
  271
  272'/'(Free, Lambda, A1, A2, A3, A4, A5, A6) :-
  273    lambda_free(Free),
  274    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  275    call(LambdaCopy, A1, A2, A3, A4, A5, A6).
  276
  277'/'(Free, Lambda, A1, A2, A3, A4, A5, A6, A7) :-
  278    lambda_free(Free),
  279    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  280    call(LambdaCopy, A1, A2, A3, A4, A5, A6, A7).



 unify_lambda_parameters(+ParmsAndFree, +Args, -CallArgs, +Lambda, -LambdaCopy) is det





Arguments:





ParmsAndFree- is the first argumen of >>, either a list
of parameters or a term {Free}/Params.


Args- is a list of input parameters, args 3.. from >>


CallArgs- are the calling arguments for the Lambda
expression. I.e., we call call(LambdaCopy, CallArgs).












  292unify_lambda_parameters(Parms, _Args, _ExtraArgs, _Lambda, _LambdaCopy) :-
  293    var(Parms),
  294    !,
  295    instantiation_error(Parms).
  296unify_lambda_parameters(Free/Parms, Args, ExtraArgs, Lambda, LambdaCopy) :-
  297    !,
  298    lambda_free(Free),
  299    must_be(list, Parms),
  300    copy_term_nat(Free/Parms>>Lambda, Free/ParmsCopy>>LambdaCopy),
  301    unify_lambda_parameters_(ParmsCopy, Args, ExtraArgs,
  302                             Free/Parms>>Lambda).
  303unify_lambda_parameters(Parms, Args, ExtraArgs, Lambda, LambdaCopy) :-
  304    must_be(list, Parms),
  305    copy_term_nat(Parms>>Lambda, ParmsCopy>>LambdaCopy),
  306    unify_lambda_parameters_(ParmsCopy, Args, ExtraArgs,
  307                             Parms>>Lambda).
  308
  309unify_lambda_parameters_([], ExtraArgs, ExtraArgs, _) :- !.
  310unify_lambda_parameters_([Parm|Parms], [Arg|Args], ExtraArgs, Culprit) :-
  311    !,
  312    Parm = Arg,
  313    unify_lambda_parameters_(Parms, Args, ExtraArgs, Culprit).
  314unify_lambda_parameters_(_,_,_,Culprit) :-
  315    domain_error(lambda_parameters, Culprit).
  316
  317lambda_free(Free) :-
  318    var(Free),
  319    !,
  320    instantiation_error(Free).
  321lambda_free({_}) :- !.
  322lambda_free({}) :- !.
  323lambda_free(Free) :-
  324    type_error(lambda_free, Free).



 expand_lambda(+Goal, -Head) is semidet
True if Goal is a sufficiently instantiated Lambda expression
that is compiled to the predicate Head. The predicate Head is
added to the current compilation context using
compile_aux_clauses/1.


  333expand_lambda(Goal, Head) :-
  334    Goal =.. ['>>', Parms, Lambda| ExtraArgs],
  335    is_callable(Lambda),
  336    nonvar(Parms),
  337    lambda_functor(Parms>>Lambda, Functor),
  338    (   Parms = Free/ExtraArgs
  339    ->  is_lambda_free(Free),
  340        free_to_list(Free, FreeList)
  341    ;   Parms = ExtraArgs,
  342        FreeList = []
  343    ),
  344    append(FreeList, ExtraArgs, Args),
  345    Head =.. [Functor|Args],
  346    compile_aux_clause_if_new(Head, Lambda).
  347expand_lambda(Goal, Head) :-
  348    Goal =.. ['/', Free, Closure|ExtraArgs],
  349    is_lambda_free(Free),
  350    is_callable(Closure),
  351    free_to_list(Free, FreeList),
  352    lambda_functor(Free/Closure, Functor),
  353    append(FreeList, ExtraArgs, Args),
  354    Head =.. [Functor|Args],
  355    Closure =.. [ClosureFunctor|ClosureArgs],
  356    append(ClosureArgs, ExtraArgs, LambdaArgs),
  357    Lambda =.. [ClosureFunctor|LambdaArgs],
  358    compile_aux_clause_if_new(Head, Lambda).
  359
  360lambda_functor(Term, Functor) :-
  361    copy_term_nat(Term, Copy),
  362    variant_sha1(Copy, Functor0),
  363    atom_concat('__aux_yall_', Functor0, Functor).
  364
  365free_to_list({}, []).
  366free_to_list({VarsConj}, Vars) :-
  367    conjunction_to_list(VarsConj, Vars).
  368
  369conjunction_to_list(Term, [Term]) :-
  370    var(Term),
  371    !.
  372conjunction_to_list((Term, Conjunction), [Term|Terms]) :-
  373    !,
  374    conjunction_to_list(Conjunction, Terms).
  375conjunction_to_list(Term, [Term]).
  376
  377compile_aux_clause_if_new(Head, Lambda) :-
  378    prolog_load_context(module, Context),
  379    (   predicate_property(Context:Head, defined)
  380    ->  true
  381    ;   compile_aux_clauses([(Head :- Lambda)])
  382    ).
  383
  384lambda_like(Goal) :-
  385    compound(Goal),
  386    compound_name_arity(Goal, Name, Arity),
  387    lambda_functor(Name),
  388    Arity >= 2.
  389
  390lambda_functor(>>).
  391lambda_functor(/).
  392
  393:- dynamic system:goal_expansion/2.  394:- multifile system:goal_expansion/2.  395
  396system:goal_expansion(Goal, Head) :-
  397    lambda_like(Goal),
  398    prolog_load_context(source, _),
  399    \+ current_prolog_flag(xref, true),
  400    expand_lambda(Goal, Head).



 is_lambda(@Term) is semidet
True if Term is a valid Lambda expression.


  406is_lambda(Term) :-
  407    compound(Term),
  408    compound_name_arguments(Term, Name, Args),
  409    is_lambda(Name, Args).
  410
  411is_lambda(>>, [Params,Lambda|_]) :-
  412    is_lamdba_params(Params),
  413    is_callable(Lambda).
  414is_lambda(/, [Free,Lambda|_]) :-
  415    is_lambda_free(Free),
  416    is_callable(Lambda).
  417
  418is_lamdba_params(Var) :-
  419    var(Var), !, fail.
  420is_lamdba_params(Free/Params) :-
  421    !,
  422    is_lambda_free(Free),
  423    is_list(Params).
  424
  425is_lambda_free(Free) :-
  426    nonvar(Free), !, (Free = {_} -> true ; Free == {}).
  427
  428is_callable(Term) :-
  429    strip_module(Term, _, Goal),
  430    callable(Goal).



 lambda_calls(+LambdaExpression, -Goal) is det


 lambda_calls(+LambdaExpression, +ExtraArgs, -Goal) is det
Goal is the goal called if call/N is applied to
LambdaExpression, where ExtraArgs are the additional arguments
to call/N. ExtraArgs can be an integer or a list of concrete
arguments. This predicate is used for cross-referencing and code
highlighting.


  442lambda_calls(LambdaExtended, Goal) :-
  443    compound(LambdaExtended),
  444    compound_name_arguments(LambdaExtended, Name, [A1,A2|Extra]),
  445    lambda_functor(Name),
  446    compound_name_arguments(Lambda, Name, [A1,A2]),
  447    lambda_calls(Lambda, Extra, Goal).
  448
  449lambda_calls(Lambda, Extra, Goal) :-
  450    integer(Extra),
  451    !,
  452    length(ExtraVars, Extra),
  453    lambda_calls_(Lambda, ExtraVars, Goal).
  454lambda_calls(Lambda, Extra, Goal) :-
  455    must_be(list, Extra),
  456    lambda_calls_(Lambda, Extra, Goal).
  457
  458lambda_calls_(Params>>Lambda, Args, Goal) :-
  459    unify_lambda_parameters(Params, Args, ExtraArgs, Lambda, LambdaCopy),
  460    extend(LambdaCopy, ExtraArgs, Goal).
  461lambda_calls_(Free/Lambda, ExtraArgs, Goal) :-
  462    copy_term_nat(Free+Lambda, Free+LambdaCopy),
  463    extend(LambdaCopy, ExtraArgs, Goal).
  464
  465extend(Var, _, _) :-
  466    var(Var),
  467    !,
  468    instantiation_error(Var).
  469extend(Cyclic, _, _) :-
  470    cyclic_term(Cyclic),
  471    !,
  472    type_error(acyclic_term, Cyclic).
  473extend(M:Goal0, Extra, M:Goal) :-
  474    !,
  475    extend(Goal0, Extra, Goal).
  476extend(Goal0, Extra, Goal) :-
  477    atom(Goal0),
  478    !,
  479    Goal =.. [Goal0|Extra].
  480extend(Goal0, Extra, Goal) :-
  481    compound(Goal0),
  482    !,
  483    compound_name_arguments(Goal0, Name, Args0),
  484    append(Args0, Extra, Args),
  485    compound_name_arguments(Goal, Name, Args).
  486
  487
  488                 /*******************************
  489                 *     SYNTAX HIGHLIGHTING      *
  490                 *******************************/
  491
  492:- multifile prolog_colour:goal_colours/2.  493
  494yall_colours(Lambda, built_in-[classify,body(Goal)|ArgSpecs]) :-
  495    catch(lambda_calls(Lambda, Goal), _, fail),
  496    Lambda =.. [>>,_,_|Args],
  497    classify_extra(Args, ArgSpecs).
  498
  499classify_extra([], []).
  500classify_extra([_|T0], [classify|T]) :-
  501    classify_extra(T0, T).
  502
  503prolog_colour:goal_colours(Goal, Spec) :-
  504    lambda_like(Goal),
  505    yall_colours(Goal, Spec).
  506
  507
  508                 /*******************************
  509                 *          XREF SUPPORT        *
  510                 *******************************/
  511
  512:- multifile prolog:called_by/4.  513
  514prolog:called_by(Lambda, yall, _, [Goal]) :-
  515    lambda_like(Lambda),
  516    catch(lambda_calls(Lambda, Goal), _, fail).
  517
  518
  519                 /*******************************
  520                 *        SANDBOX SUPPORT       *
  521                 *******************************/
  522
  523:- multifile
  524    sandbox:safe_meta_predicate/1,
  525    sandbox:safe_meta/2.  526
  527sandbox:safe_meta_predicate(yall:(/)/2).
  528sandbox:safe_meta_predicate(yall:(/)/3).
  529sandbox:safe_meta_predicate(yall:(/)/4).
  530sandbox:safe_meta_predicate(yall:(/)/5).
  531sandbox:safe_meta_predicate(yall:(/)/6).
  532sandbox:safe_meta_predicate(yall:(/)/7).
  533
  534sandbox:safe_meta(yall:Lambda, [Goal]) :-
  535    compound(Lambda),
  536    compound_name_arity(Lambda, >>, Arity),
  537    Arity >= 2,
  538    lambda_calls(Lambda, Goal)