/* Part of SWI-Prolog
Author: Paulo Moura
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2015, Paulo Moura, Kyndi Inc., VU University Amsterdam
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 THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"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 THE
COPYRIGHT OWNER 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.
*/
:- module(yall,
[ (>>)/2, (>>)/3, (>>)/4, (>>)/5, (>>)/6, (>>)/7, (>>)/8, (>>)/9,
(/)/2, (/)/3, (/)/4, (/)/5, (/)/6, (/)/7, (/)/8, (/)/9,
lambda_calls/2, % +LambdaExt, -Goal
lambda_calls/3, % +Lambda, +Args, -Goal
is_lambda/1 % @Term
]).
:- autoload(library(error),
[ instantiation_error/1,
must_be/2,
domain_error/2,
type_error/2
]).
:- autoload(library(lists),[append/3]).
:- meta_predicate
'>>'(?, 0),
'>>'(?, :, ?),
'>>'(?, :, ?, ?),
'>>'(?, :, ?, ?, ?),
'>>'(?, :, ?, ?, ?, ?),
'>>'(?, :, ?, ?, ?, ?, ?),
'>>'(?, :, ?, ?, ?, ?, ?, ?),
'>>'(?, :, ?, ?, ?, ?, ?, ?, ?).
:- meta_predicate
'/'(?, 0),
'/'(?, 1, ?),
'/'(?, 2, ?, ?),
'/'(?, 3, ?, ?, ?),
'/'(?, 4, ?, ?, ?, ?),
'/'(?, 5, ?, ?, ?, ?, ?),
'/'(?, 6, ?, ?, ?, ?, ?, ?),
'/'(?, 7, ?, ?, ?, ?, ?, ?, ?).
/** <module> 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/2-5
family or foldl/4-7.
The _closure_ concept used here is somewhat different from the closure
concept from functional programming. The latter is a function that is
always evaluated in the context that existed at function creation time.
Here, a closure is a term of arity _0 =< L =< K_. The term's functor is
the name of a predicate of arity _K_ and the term's _L_ arguments (where
_L_ could be 0) correspond to _L_ leftmost arguments of said predicate,
bound to parameter values. For example, a closure involving
atom_concat/3 might be the term atom_concat(prefix). In order of
increasing _L_, one would have increasingly more complete closures that
could be passed to call/3, all giving the same result:
```
call(atom_concat,prefix,suffix,R).
call(atom_concat(prefix),suffix,R).
call(atom_concat(prefix,suffix),R).
call(atom_concat(prefix,suffix,R)).
```
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(atom_concat(Postfix),ListIn,ListOut) calls
atom_concat(Postfix,In,Out). This is where library(yall) comes in, where
the module name, _yall_, stands for _Yet Another Lambda Library_.
The library allows us to write a lambda expression that _wraps around_
the (possibly complex) goal to call:
```
?- maplist([In,Out]>>atom_concat(In,'_p',Out), [a,b], ListOut).
ListOut = [a_p, b_p].
```
A bracy list `{...}` specifies which variables are _shared_ between the
wrapped goal and the surrounding context. This allows us to write the
code below. Without the `{Postfix}` a fresh 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 confine variables to the called goal's context. This features
shines when combined with bagof/3 or setof/3 where one normally has to
list those variables whose bindings one is _not_ interested in using the
`Var^Goal` construct (marking `Var` as existentially quantified and
confining it to the called goal's context). Lambda expressions allow you
to do the converse: specify the variables which one _is_ interested in.
These variables are common to the context of the called goal and the
surrounding context.
Lambda expressions use the syntax below
```
{...}/[...]>>Goal.
```
The `{...}` optional part is used for lambda-free variables (the ones
shared between contexts). 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.
This module implements [Logtalk's lambda expressions
syntax](https://logtalk.org/manuals/refman/grammar.html#lambda-expressions).
The development of this module was sponsored by Kyndi, Inc.
@tbd Extend optimization support
@author Paulo Moura and Jan Wielemaker
*/
%! >>(+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:
%
% - The first length(Parameters) arguments from A1, ... are
% unified with (a copy of) Parameters, which _may_ share
% them with variables in Lambda.
% - Possible excess arguments are passed by position.
%
% @arg 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.
'>>'(Parms, Lambda) :-
unify_lambda_parameters(Parms, [],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1) :-
unify_lambda_parameters(Parms, [A1],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2) :-
unify_lambda_parameters(Parms, [A1,A2],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2, A3) :-
unify_lambda_parameters(Parms, [A1,A2,A3],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2, A3, A4) :-
unify_lambda_parameters(Parms, [A1,A2,A3,A4],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2, A3, A4, A5) :-
unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2, A3, A4, A5, A6) :-
unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5,A6],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
call(Goal).
'>>'(Parms, Lambda, A1, A2, A3, A4, A5, A6, A7) :-
unify_lambda_parameters(Parms, [A1,A2,A3,A4,A5,A6,A7],
ExtraArgs, Lambda, LambdaCopy),
Goal =.. [call, LambdaCopy| ExtraArgs],
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)
% ==
'/'(Free, Lambda) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy).
'/'(Free, Lambda, A1) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1).
'/'(Free, Lambda, A1, A2) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2).
'/'(Free, Lambda, A1, A2, A3) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2, A3).
'/'(Free, Lambda, A1, A2, A3, A4) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2, A3, A4).
'/'(Free, Lambda, A1, A2, A3, A4, A5) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2, A3, A4, A5).
'/'(Free, Lambda, A1, A2, A3, A4, A5, A6) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2, A3, A4, A5, A6).
'/'(Free, Lambda, A1, A2, A3, A4, A5, A6, A7) :-
lambda_free(Free),
copy_term_nat(Free+Lambda, Free+LambdaCopy),
call(LambdaCopy, A1, A2, A3, A4, A5, A6, A7).
%! unify_lambda_parameters(+ParmsAndFree, +Args, -CallArgs,
%! +Lambda, -LambdaCopy) is det.
%
% @arg ParmsAndFree is the first argumen of `>>`, either a list
% of parameters or a term `{Free}/Params`.
% @arg Args is a list of input parameters, args 3.. from `>>`
% @arg CallArgs are the calling arguments for the Lambda
% expression. I.e., we call call(LambdaCopy, CallArgs).
unify_lambda_parameters(Parms, _Args, _ExtraArgs, _Lambda, _LambdaCopy) :-
var(Parms),
!,
instantiation_error(Parms).
unify_lambda_parameters(Free/Parms, Args, ExtraArgs, Lambda, LambdaCopy) :-
!,
lambda_free(Free),
must_be(list, Parms),
copy_term_nat(Free/Parms>>Lambda, Free/ParmsCopy>>LambdaCopy),
unify_lambda_parameters_(ParmsCopy, Args, ExtraArgs,
Free/Parms>>Lambda).
unify_lambda_parameters(Parms, Args, ExtraArgs, Lambda, LambdaCopy) :-
must_be(list, Parms),
copy_term_nat(Parms>>Lambda, ParmsCopy>>LambdaCopy),
unify_lambda_parameters_(ParmsCopy, Args, ExtraArgs,
Parms>>Lambda).
unify_lambda_parameters_([], ExtraArgs, ExtraArgs, _) :- !.
unify_lambda_parameters_([Parm|Parms], [Arg|Args], ExtraArgs, Culprit) :-
!,
Parm = Arg,
unify_lambda_parameters_(Parms, Args, ExtraArgs, Culprit).
unify_lambda_parameters_(_,_,_,Culprit) :-
domain_error(lambda_parameters, Culprit).
lambda_free(Free) :-
var(Free),
!,
instantiation_error(Free).
lambda_free({_}) :- !.
lambda_free({}) :- !.
lambda_free(Free) :-
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.
expand_lambda(Goal, Head) :-
Goal =.. ['>>', Parms, Lambda| ExtraArgs],
is_callable(Lambda),
nonvar(Parms),
lambda_functor(Parms>>Lambda, Functor),
( Parms = Free/ExtraArgs
-> is_lambda_free(Free),
free_to_list(Free, FreeList)
; Parms = ExtraArgs,
FreeList = []
),
append(FreeList, ExtraArgs, Args),
Head =.. [Functor|Args],
compile_aux_clause_if_new(Head, Lambda).
expand_lambda(Goal, Head) :-
Goal =.. ['/', Free, Closure|ExtraArgs],
is_lambda_free(Free),
is_callable(Closure),
free_to_list(Free, FreeList),
lambda_functor(Free/Closure, Functor),
append(FreeList, ExtraArgs, Args),
Head =.. [Functor|Args],
Closure =.. [ClosureFunctor|ClosureArgs],
append(ClosureArgs, ExtraArgs, LambdaArgs),
Lambda =.. [ClosureFunctor|LambdaArgs],
compile_aux_clause_if_new(Head, Lambda).
lambda_functor(Term, Functor) :-
copy_term_nat(Term, Copy),
variant_sha1(Copy, Functor0),
atom_concat('__aux_yall_', Functor0, Functor).
free_to_list({}, []).
free_to_list({VarsConj}, Vars) :-
conjunction_to_list(VarsConj, Vars).
conjunction_to_list(Term, [Term]) :-
var(Term),
!.
conjunction_to_list((Term, Conjunction), [Term|Terms]) :-
!,
conjunction_to_list(Conjunction, Terms).
conjunction_to_list(Term, [Term]).
compile_aux_clause_if_new(Head, Lambda) :-
prolog_load_context(module, Context),
( predicate_property(Context:Head, defined)
-> true
; expand_goal(Lambda, LambdaExpanded),
compile_aux_clauses([(Head :- LambdaExpanded)])
).
lambda_like(Goal) :-
compound(Goal),
compound_name_arity(Goal, Name, Arity),
lambda_functor(Name),
Arity >= 2.
lambda_functor(>>).
lambda_functor(/).
:- dynamic system:goal_expansion/2.
:- multifile system:goal_expansion/2.
system:goal_expansion(Goal, Head) :-
lambda_like(Goal),
prolog_load_context(source, _),
\+ current_prolog_flag(xref, true),
expand_lambda(Goal, Head).
%! is_lambda(@Term) is semidet.
%
% True if Term is a valid Lambda expression.
is_lambda(Term) :-
compound(Term),
compound_name_arguments(Term, Name, Args),
is_lambda(Name, Args).
is_lambda(>>, [Params,Lambda|_]) :-
is_lamdba_params(Params),
is_callable(Lambda).
is_lambda(/, [Free,Lambda|_]) :-
is_lambda_free(Free),
is_callable(Lambda).
is_lamdba_params(Var) :-
var(Var), !, fail.
is_lamdba_params(Free/Params) :-
!,
is_lambda_free(Free),
is_list(Params).
is_lamdba_params(Params) :-
is_list(Params).
is_lambda_free(Free) :-
nonvar(Free), !, (Free = {_} -> true ; Free == {}).
is_callable(Term) :-
strip_module(Term, _, Goal),
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.
lambda_calls(LambdaExtended, Goal) :-
compound(LambdaExtended),
compound_name_arguments(LambdaExtended, Name, [A1,A2|Extra]),
lambda_functor(Name),
compound_name_arguments(Lambda, Name, [A1,A2]),
lambda_calls(Lambda, Extra, Goal).
lambda_calls(Lambda, Extra, Goal) :-
integer(Extra),
!,
length(ExtraVars, Extra),
lambda_calls_(Lambda, ExtraVars, Goal).
lambda_calls(Lambda, Extra, Goal) :-
must_be(list, Extra),
lambda_calls_(Lambda, Extra, Goal).
lambda_calls_(Params>>Lambda, Args, Goal) :-
unify_lambda_parameters(Params, Args, ExtraArgs, Lambda, LambdaCopy),
extend(LambdaCopy, ExtraArgs, Goal).
lambda_calls_(Free/Lambda, ExtraArgs, Goal) :-
copy_term_nat(Free+Lambda, Free+LambdaCopy),
extend(LambdaCopy, ExtraArgs, Goal).
extend(Var, _, _) :-
var(Var),
!,
instantiation_error(Var).
extend(Cyclic, _, _) :-
cyclic_term(Cyclic),
!,
type_error(acyclic_term, Cyclic).
extend(M:Goal0, Extra, M:Goal) :-
!,
extend(Goal0, Extra, Goal).
extend(Goal0, Extra, Goal) :-
atom(Goal0),
!,
Goal =.. [Goal0|Extra].
extend(Goal0, Extra, Goal) :-
compound(Goal0),
!,
compound_name_arguments(Goal0, Name, Args0),
append(Args0, Extra, Args),
compound_name_arguments(Goal, Name, Args).
/*******************************
* SYNTAX HIGHLIGHTING *
*******************************/
:- multifile prolog_colour:goal_colours/2.
yall_colours(Lambda, built_in-[classify,body(Goal)|ArgSpecs]) :-
catch(lambda_calls(Lambda, Goal), _, fail),
Lambda =.. [>>,_,_|Args],
classify_extra(Args, ArgSpecs).
classify_extra([], []).
classify_extra([_|T0], [classify|T]) :-
classify_extra(T0, T).
prolog_colour:goal_colours(Goal, Spec) :-
lambda_like(Goal),
yall_colours(Goal, Spec).
/*******************************
* XREF SUPPORT *
*******************************/
:- multifile prolog:called_by/4.
prolog:called_by(Lambda, yall, _, [Goal]) :-
lambda_like(Lambda),
catch(lambda_calls(Lambda, Goal), _, fail).
/*******************************
* SANDBOX SUPPORT *
*******************************/
:- multifile
sandbox:safe_meta_predicate/1,
sandbox:safe_meta/2.
sandbox:safe_meta_predicate(yall:(/)/2).
sandbox:safe_meta_predicate(yall:(/)/3).
sandbox:safe_meta_predicate(yall:(/)/4).
sandbox:safe_meta_predicate(yall:(/)/5).
sandbox:safe_meta_predicate(yall:(/)/6).
sandbox:safe_meta_predicate(yall:(/)/7).
sandbox:safe_meta(yall:Lambda, [Goal]) :-
compound(Lambda),
compound_name_arity(Lambda, >>, Arity),
Arity >= 2,
lambda_calls(Lambda, Goal).