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#############################################################################
##
## This file is part of GAP, a system for computational discrete algebra.
## This file's authors include Frank Celler, Martin Schönert.
##
## Copyright of GAP belongs to its developers, whose names are too numerous
## to list here. Please refer to the COPYRIGHT file for details.
##
## SPDX-License-Identifier: GPL-2.0-or-later
##
## This file defines the less frequently used functions to select
## methods. More frequently used functions used to be in methsel1.g,
## which was compiled in the default setup; this code has now been
## replaced by hand written C code in the kernel.
##
#############################################################################
##
#F # # # # # # # # # # # # # method selection # # # # # # # # # # # # # # #
##
#############################################################################
##
#F AttributeValueNotSet( <attr>, <obj> )
##
BIND_GLOBAL( "AttributeValueNotSet", function(attr,obj)
local type,fam,methods,i,j,flag,erg;
type:=TypeObj(obj);
fam:=FamilyObj(obj);
methods:=METHODS_OPERATION(attr,1);
for i in [1..LEN_LIST(methods)/(1+BASE_SIZE_METHODS_OPER_ENTRY)] do
j:=(1+BASE_SIZE_METHODS_OPER_ENTRY)*(i-1);
flag:=true;
flag:=flag and IS_SUBSET_FLAGS(type![2],methods[j+2]);
if flag then
flag:=flag and methods[j+1](fam);
fi;
if flag then
attr:=methods[j+3];
erg:=attr(obj);
if not IS_IDENTICAL_OBJ(erg,TRY_NEXT_METHOD) then
return erg;
fi;
fi;
od;
Error("No applicable method found for attribute");
end );
#############################################################################
##
#F # # # # # # # # # # # verbose method selection # # # # # # # # # # # # #
##
BIND_GLOBAL( "VMETHOD_PRINT_INFO", function ( methods, i, arity)
local offset;
offset := (arity+BASE_SIZE_METHODS_OPER_ENTRY)*(i-1)+arity;
Print("#I ", methods[offset+4],
" at ", methods[offset+5][1], ":", methods[offset+5][2], "\n");
end );
#############################################################################
##
#F # # # # # # # # # # # verbose try next method # # # # # # # # # # # # #
##
BIND_GLOBAL( "NEXT_VMETHOD_PRINT_INFO", function ( methods, i, arity)
local offset;
offset := (arity+BASE_SIZE_METHODS_OPER_ENTRY)*(i-1)+arity;
Print("#I Trying next: ", methods[offset+4],
" at ", methods[offset+5][1], ":", methods[offset+5][2], "\n");
end );
#############################################################################
##
#F NewTagBasedOperation( <name>, <requirements> )
#F DeclareTagBasedOperation( <name>, <requirements> )
#F InstallTagBasedMethod( <oper>[, <tag>], <meth> )
##
## <#GAPDoc Label="DeclareTagBasedOperation">
## <ManSection>
## <Heading>Tag Based Operations</Heading>
## <Func Name="NewTagBasedOperation" Arg='name, requirements'/>
## <Func Name="DeclareTagBasedOperation" Arg='name, requirements'/>
## <Func Name="InstallTagBasedMethod" Arg='oper[, tag], meth'/>
##
## <Description>
## <Ref Func="NewTagBasedOperation"/> returns an operation with name
## <A>name</A> that is declared as <E>tag based</E>
## w.r.t. the list <A>requirements</A> of filters for its arguments.
## If an operation with name <A>name</A> exists already before the call
## then this operation is returned, otherwise a new operation gets created.
## <P/>
## <Ref Func="DeclareTagBasedOperation"/> does the same and additionally
## binds the returned operation to the global variable <A>name</A> if the
## operation is new.
## <P/>
## Declaring the operation <A>oper</A> as tag based w.r.t.
## <A>requirements</A> means that <Ref Func="InstallTagBasedMethod"/>
## can be used to install the method <A>meth</A> for <A>oper</A>,
## a function whose arguments satisfy <A>requirements</A>,
## with the following meaning.
## <P/>
## <List>
## <Item>
## The method <A>meth</A> is applicable if the first argument
## of the call to <A>oper</A> is identical (in the sense of
## <Ref Func="IsIdenticalObj"/>) with the tag <A>tag</A> that has been
## specified in the <Ref Func="InstallTagBasedMethod"/> call.
## </Item>
## <Item>
## If none of the tag based methods for <A>oper</A> has a <A>tag</A>
## that is identical with the first argument of the call to <A>oper</A>
## and if there is a tag based method for <A>oper</A> for which no
## <A>tag</A> was specified then this method is applicable.
## </Item>
## </List>
## <P/>
## Thus at most <E>one</E> tag based method for <A>oper</A> is applicable,
## and if a method without <A>tag</A> has been installed then it serves as
## the default method.
## This is in contrast to the situation with constructors
## (see <Ref Sect="Constructors"/>) where the first argument is a filter
## that is used as a tag, but several methods can be applicable in a call
## to a constructor and one cannot define a default method for it.
## <P/>
## Typical use cases for tag based operations are operations that shall
## create objects in particular internal representations; the filters that
## define these representations are then used as the first argument,
## and one wants that either the unique method that belongs to this filter
## or a default method is called.
## <P/>
## Currently it is possible to declare an operation as tag based
## only for <E>one</E> list of requirements.
## <P/>
## Installing methods with <Ref Func="InstallMethod"/> for a tag based
## operation is possible.
## However, installing such methods with the same requirements as the ones
## for the tag based methods will have no effect because the handling of
## tag based methods gets installed with <Ref Func="InstallEarlyMethod"/>
## and thus has higher priority.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
BIND_GLOBAL( "_METHODS_TAG_BASED", OBJ_MAP() );
BIND_GLOBAL( "_METHODS_TAG_BASED_DEFAULTS", OBJ_MAP() );
BIND_GLOBAL( "NewTagBasedOperation",
function( name, requirements )
local oper, methods;
# get the operation
if ISBOUND_GLOBAL( name ) then
oper:= VALUE_GLOBAL( name );
DeclareOperation( name, requirements );
else
oper:= NewOperation( name, requirements );
fi;
# initialize the tag handling for 'oper'
if FIND_OBJ_MAP( _METHODS_TAG_BASED, oper, fail ) <> fail then
Error( "operation <oper> has already been declared as tag based" );
fi;
methods:= OBJ_MAP();
ADD_OBJ_MAP( _METHODS_TAG_BASED, oper, methods );
ADD_OBJ_MAP( _METHODS_TAG_BASED_DEFAULTS, oper, requirements );
# install the method for 'oper' that uses the tag handling
if LENGTH( requirements ) = 1 then
InstallEarlyMethod( oper,
function( req1 )
local method;
if not requirements[1]( req1 ) then
TryNextMethod();
fi;
method:= FIND_OBJ_MAP( methods, req1, fail );
if method = fail then
# Take the default method if there is one.
method:= FIND_OBJ_MAP( methods, IS_OBJECT, fail );
fi;
if method = fail then
Error( "no default installed for tag based operation <oper>" );
fi;
return method( req1 );
end );
elif LENGTH( requirements ) = 2 then
InstallEarlyMethod( oper,
function( req1, req2 )
local method;
if not ( requirements[1]( req1 ) and
requirements[2]( req2 ) ) then
TryNextMethod();
fi;
method:= FIND_OBJ_MAP( methods, req1, fail );
if method = fail then
# Take the default method if there is one.
method:= FIND_OBJ_MAP( methods, IS_OBJECT, fail );
fi;
if method = fail then
Error( "no default installed for tag based operation <oper>" );
fi;
return method( req1, req2 );
end );
elif LENGTH( requirements ) = 3 then
InstallEarlyMethod( oper,
function( req1, req2, req3 )
local method;
if not ( requirements[1]( req1 ) and
requirements[2]( req2 ) and
requirements[3]( req3 ) ) then
TryNextMethod();
fi;
method:= FIND_OBJ_MAP( methods, req1, fail );
if method = fail then
# Take the default method if there is one.
method:= FIND_OBJ_MAP( methods, IS_OBJECT, fail );
fi;
if method = fail then
Error( "no default installed for tag based operation <oper>" );
fi;
return method( req1, req2, req3 );
end );
elif LENGTH( requirements ) = 4 then
InstallEarlyMethod( oper,
function( req1, req2, req3, req4 )
local method;
if not ( requirements[1]( req1 ) and
requirements[2]( req2 ) and
requirements[3]( req3 ) and
requirements[4]( req4 ) ) then
TryNextMethod();
fi;
method:= FIND_OBJ_MAP( methods, req1, fail );
if method = fail then
# Take the default method if there is one.
method:= FIND_OBJ_MAP( methods, IS_OBJECT, fail );
fi;
if method = fail then
Error( "no default installed for tag based operation <oper>" );
fi;
return method( req1, req2, req3, req4 );
end );
else
Error( "tag based operations for ", LENGTH( requirements ),
" arguments are currently not supported" );
fi;
return oper;
end );
BIND_GLOBAL( "DeclareTagBasedOperation",
function( name, requirements )
local oper;
oper:= NewTagBasedOperation( name, requirements );
if not ISBOUND_GLOBAL( name ) then
BIND_GLOBAL( name, oper );
fi;
end );
BIND_GLOBAL( "InstallTagBasedMethod", function( oper, meth... )
local dict, defaultdata, tag, n;
dict:= FIND_OBJ_MAP( _METHODS_TAG_BASED, oper, fail );
if dict = fail then
Error( "<oper> is not declared as tag based operation" );
fi;
defaultdata:= FIND_OBJ_MAP( _METHODS_TAG_BASED_DEFAULTS, oper, fail );
if defaultdata = fail then
Error( "this should not happen" );
fi;
if LENGTH( meth ) = 1 then
tag:= IS_OBJECT;
meth:= meth[1];
elif LENGTH( meth ) = 2 then
tag:= meth[1];
meth:= meth[2];
else
Error( "usage: InstallTagBasedMethod( oper[, tag], meth )" );
fi;
if not REREADING and FIND_OBJ_MAP( dict, tag, fail ) <> fail then
Error( "<tag> has already been set in <dict>" );
elif not IS_FUNCTION( meth ) then
Error( "<meth> must be a function" );
fi;
n:= NARG_FUNC( meth );
if n > 0 and n <> LENGTH( defaultdata ) then
Error( "<meth> must take ", LENGTH( defaultdata ), " arguments" );
fi;
ADD_OBJ_MAP( dict, tag, meth );
end );
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