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#############################################################################
##
#W global.g GAP library Steve Linton
##
#H @(#)$Id: global.g,v 4.10 2002/04/15 10:04:42 sal Exp $
##
#Y Copyright (C) 1996, Lehrstuhl D fuer Mathematik, RWTH Aachen, Germany
#Y (C) 1998 School Math and Comp. Sci., University of St. Andrews, Scotland
#Y Copyright (C) 2002 The GAP Group
##
##
## This file contains the first stage of the "public" interface to
## the global variable namespace, allowing globals to be accessed and
## set by name.
##
## This is defined in two stages. This file defines "capitalized" versions
## of the functions which do not use Info or other niceties and are not
## set up with InstallGlobalFunction. This can thus be read early, and
## the functions it defines can be used to define functions used to read
## more of the library.
##
## The global.gd and global.gi stages will install the really "public"
## functions and can be read later (once Info, DeclareGlobalFunction,
## etc are there)
##
Revision.global_g :=
"@(#)$Id: global.g,v 4.10 2002/04/15 10:04:42 sal Exp $";
#############################################################################
##
#F VALUE_GLOBAL ( <name> ) . . . . . . . . . . .access a global by its name
##
## VALUE_GLOBAL ( <name> ) returns the value currently bound to the global
## variable named by the string <name>. An error is raised if no value
## is currently bound
##
VALUE_GLOBAL := VAL_GVAR;
#############################################################################
##
#F ISBOUND_GLOBAL ( <name> ) . . . . check if a global is bound by its name
##
## ISBOUND_GLOBAL ( <name> ) returns true if a value currently bound
## to the global variable named by the string <name> and false otherwise
##
ISBOUND_GLOBAL := ISB_GVAR;
#############################################################################
##
#F UNBIND_GLOBAL ( <name> ) . . . . . . . . . .unbind a global by its name
##
## UNBIND_GLOBAL ( <name> ) removes any value currently bound
## to the global variable named by the string <name>. Nothing is returned.
##
## The global variable named by <name> must be writable,
## otherwise an error is raised.
##
UNBIND_GLOBAL := UNB_GVAR;
#############################################################################
##
#F IS_READ_ONLY_GLOBAL ( <name> ) determine if a global variable is read-only
##
## IS_READ_ONLY_GLOBAL ( <name> ) returns true if the global variable
## named by the string <name> is read-only and false otherwise (the default)
##
IS_READ_ONLY_GLOBAL := IsReadOnlyGVar;
#############################################################################
##
#F MAKE_READ_ONLY_GLOBAL ( <name> ) . . . . make a global variable read-only
##
## MAKE_READ_ONLY_GLOBAL ( <name> ) marks the global variable named
## by the string <name> as read-only.
##
MAKE_READ_ONLY_GLOBAL := MakeReadOnlyGVar;
#############################################################################
##
#F MAKE_READ_WRITE_GLOBAL ( <name> ) . . .make a global variable read-write
##
## MAKE_READ_WRITE_GLOBAL ( <name> ) marks the global variable named
## by the string <name> as read-write
##
MAKE_READ_WRITE_GLOBAL := MakeReadWriteGVar;
#############################################################################
##
#V REREADING set to true inside a Reread, changes much
## behaviour
##
REREADING := false;
MAKE_READ_ONLY_GLOBAL("REREADING");
#############################################################################
##
#F BIND_GLOBAL ( <name>, <val> ) . . . . . .sets a global variable 'safely'
##
## BIND_GLOBAL ( <name>, <val> ) sets the global variable named by
## the string <name> to the value <val>, provided it was previously
## unbound, and makes it read-only. This is intended to be the normal
## way to create and set "official" global variable (such as
## Operations and Categories)
##
BIND_GLOBAL := function( name, val)
if not REREADING and ISBOUND_GLOBAL( name ) then
if (IS_READ_ONLY_GLOBAL(name)) then
Error("BIND_GLOBAL: variable `", name, "' must be unbound");
else
Print("#W BIND_GLOBAL: variable `", name,"' already has a value\n");
fi;
fi;
ASS_GVAR(name, val);
MAKE_READ_ONLY_GLOBAL(name);
return val;
end;
#############################################################################
##
#E global.g . . . . . . . . . . . . . . . . . . . . . . . . . . . ends here
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