#############################################################################
##
#W  global.gi                   GAP library                      Steve Linton
##
#H  @(#)$Id: global.gi,v 4.13 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 second 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. global.g 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.
##
##  This file and global.gd   install the really "public"
##  functions and can be read later (once Info, DeclareGlobalFunction,
##  etc are there)
##
##  All of these functions give a warning at level 2 if the global
##  variable name contains characters not recognised as part of
##  identifiers by the GAP parser
##
##  Functions that read data give Info messages at level 3 for InfoGlobal
##  Functions that change data give Info messages at level 2 for InfoGlobal
##

Revision.global_gi :=
    "@(#)$Id: global.gi,v 4.13 2002/04/15 10:04:42 sal Exp $";

#############################################################################
##
#I  InfoGlobal  . . . . . . . . . . . . . . . . . . information message class
##

DeclareInfoClass("InfoGlobal");

#############################################################################
##
#V  IdentifierLetters . . . . . . . .characters allowed in normal identifiers
##                               
##  This is used to produce warning messages when the XxxxGlobal functions
##  are applied to a name which could not be read in by the parser without
##  escapes
##

IdentifierLetters := 
  "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_";

#############################################################################
##
#F  IsValidIdentifier( <str> ) . . .  check if a string is a valid identifier
##

InstallGlobalFunction("IsValidIdentifier", function(str)
    return ForAll(str, c -> c in IdentifierLetters) and
           ForAny(str, c -> not (c in "0123456789") );
end);

#############################################################################
##
#F  CheckGlobalName( <name> ) . . . check global variable name -- warn if odd
##
##

CheckGlobalName := function( name )
    if ForAny(name, l -> not l in IdentifierLetters) then
        Info(InfoWarning + InfoGlobal, 2, 
             "suspicious global variable name ", name);
    fi;
end;

#############################################################################
##
#M  ValueGlobal ( <name> )  . . . . . . . . . . . access a global by its name
## 
##  ValueGlobal ( <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
##

InstallGlobalFunction( ValueGlobal, 
        function (name)
    local val;
    CheckGlobalName( name );
    val := VALUE_GLOBAL(name);
    Info( InfoGlobal, 3, "ValueGlobal: access to ",name," returned ",val); 
    return val;
end);


#############################################################################
##
#M  IsBoundGlobal ( <name> )  . . . .  check if a global is bound by its name
## 
##  IsBoundGlobal ( <name> ) returns true if a value currently bound
##  to the global variable named by the string <name> and false otherwise
##


InstallGlobalFunction( IsBoundGlobal, 
        function (name)
    local isbound;
    CheckGlobalName( name );
    isbound := ISBOUND_GLOBAL(name);
    Info( InfoGlobal, 3, 
          "IsBoundGlobal: called for ", name, " returned ", isbound);
    return isbound;
end);



#############################################################################
##
#M  UnbindGlobal ( <name> ) . . . . . . . . . .  unbind a global  by its name
## 
##  UnbindGlobal ( <name> ) removes any value currently bound
##  to the global variable named by the string <name>. Nothing is returned
##
##  A warning is given isf <name> was not bound
##  The global variable named by <name> must be writable,
##  otherwise an error is raised.
## 

InstallGlobalFunction( UnbindGlobal, 
        function (name)
    CheckGlobalName( name );
    if not ISBOUND_GLOBAL( name ) then
        Info( InfoWarning + InfoGlobal, 1, 
              "UnbindGlobal: ", name, " already unbound");
    fi;
    Info( InfoGlobal, 2, "UnbindGlobal: called for ", name);
    UNBIND_GLOBAL( name );
end);


#############################################################################
##
#F  IsReadOnlyGlobal ( <name> ) . determine if a global variable is read-only
##
##  IsReadOnlyGlobal ( <name> ) returns true if the global variable
##  named by the string <name> is read-only and false otherwise (the default)
##

InstallGlobalFunction( IsReadOnlyGlobal, 
        function (name)
    local isro;
    CheckGlobalName( name );
    isro := IS_READ_ONLY_GLOBAL(name);
    Info( InfoGlobal, 3, 
          "IsReadOnlyGlobal: called for ", name, " returned ", isro);
    return isro;
end);


#############################################################################
##
#F  MakeReadOnlyGlobal ( <name> ) . . . . .  make a global variable read-only
##
##  MakeReadOnlyGlobal ( <name> ) marks the global variable named
##  by the string <name> as read-only. 
##
##  A warning is given if <name> has no value bound to it or if it is
##  already read-only
##

InstallGlobalFunction( MakeReadOnlyGlobal, 
        function (name)
    CheckGlobalName( name );
    if name in ["time", "last", "last2", "last3", "~"] then
        Error("Making ",name," read-only is not a good idea!");
    fi;
    if not ISBOUND_GLOBAL( name ) then
        Info( InfoWarning + InfoGlobal, 1, 
              "MakeReadOnlyGlobal: ", name, " no value bound");
    fi;
    if IS_READ_ONLY_GLOBAL( name ) then
        Info( InfoWarning + InfoGlobal, 1, 
              "MakeReadOnlyGlobal: ", name, " already read-only");
    fi;
    Info( InfoGlobal, 2, "MakeReadOnlyGlobal: called for ", name);
    MAKE_READ_ONLY_GLOBAL( name );
end);


#############################################################################
##
#F  MakeReadWriteGlobal ( <name> )  . . . . make a global variable read-write
##
##  MakeReadWriteGlobal ( <name> ) marks the global variable named
##  by the string <name> as read-write
##
## A warning is given if <name> is already read-write
##

InstallGlobalFunction( MakeReadWriteGlobal, 
        function (name)
    CheckGlobalName( name );
    if not IS_READ_ONLY_GLOBAL( name ) then
        Info( InfoWarning + InfoGlobal, 1, 
              "MakeReadWriteGlobal: ", name, "already read-write");
    fi;
    Info( InfoGlobal, 2, "MakeReadWriteGlobal: called for ", name);
    MAKE_READ_WRITE_GLOBAL( name );
end);


#############################################################################
##
#F  BindGlobal ( <name>, <val> )  . . . . . . sets a global variable 'safely'
##
##  BindGlobal ( <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)
##
##  An error is given if <name> already had a value bound.
##  

InstallGlobalFunction( BindGlobal, 
        function (name, value)
    CheckGlobalName( name );
    Info( InfoGlobal, 2, "BindGlobal: called to set ", name, " to ", value);
    BIND_GLOBAL( name, value );
end);

#############################################################################
##
#F  TemporaryGlobalVarName( [<prefix>] )   name of an unbound global variable
##
##  TemporaryGlobalVarName ( [<prefix>]  ) returns a string  that can be used
##  as the  name  of a global  variable  that is not bound   at the time when
##  TemporaryGlobalVarName()  is called.    The optional  argument prefix can
##  specify a string with which the name of the global variable starts.
##

InstallGlobalFunction( TemporaryGlobalVarName,
        function( arg )
    local   prefix,  nr,  gvar;

    if Length(arg) = 0 then
        prefix := "TEMP";
    elif Length(arg) = 1 and IsString( arg[1] ) then
        prefix := arg[1];
        CheckGlobalName( prefix );
    else
        return Error( "usage: TemporaryGlobalVarName( [<prefix>] )" );
    fi;

    nr := 0;
    gvar:= prefix;
    while ISBOUND_GLOBAL( gvar ) do
        nr := nr + 1;
        gvar := Concatenation( prefix, String(nr) );
    od;

    return gvar;
end );


HIDDEN_GVARS:=[];

InstallGlobalFunction(HideGlobalVariables,function(arg)
local p,i;
  p:=Length(HIDDEN_GVARS);
  for i in arg do
    if IsString(i) then
      p:=p+1;
      HIDDEN_GVARS[p]:=i;
      p:=p+2;
      if ISBOUND_GLOBAL(i) then
        # variable is assigned
	HIDDEN_GVARS[p-1]:=VALUE_GLOBAL(i);
	if IS_READ_ONLY_GLOBAL(i) then
	  HIDDEN_GVARS[p]:=true;
	  MAKE_READ_WRITE_GLOBAL(i);
	else
	  HIDDEN_GVARS[p]:=false;
        fi;
      else
        HIDDEN_GVARS[p-1]:=fail; # needs to be assigned
        HIDDEN_GVARS[p]:=fail;
      fi;
      # temporarily remove the variable
      UNBIND_GLOBAL(i);
    else
      Error("HideGlobalVariables requires the names as strings");
    fi;
  od;
end);

InstallGlobalFunction(UnhideGlobalVariables,function(arg)
local p,str,all,l,which;
  all:=Length(arg)=0; # doe we want to unhide all?
  which:=arg;
  l:=Length(HIDDEN_GVARS);
  p:=l-2;
  while p>0 do
    str:=HIDDEN_GVARS[p];
    # do we want to unhide the variable?
    if all or str in which then
      # remove the value
      if ISBOUND_GLOBAL(str) then
	if IS_READ_ONLY_GLOBAL(str) then
	  MAKE_READ_WRITE_GLOBAL(str);
	fi;
	UNBIND_GLOBAL(str);
      fi;

      if HIDDEN_GVARS[p+2]<>fail then
	#reassign a value
	ASS_GVAR(str,HIDDEN_GVARS[p+1]);
	if HIDDEN_GVARS[p+2]=true then
	  MAKE_READ_ONLY_GLOBAL(str);
	fi;
      fi;

      # remove the corresponding "HIDDEN_GVARS" entry
      if not all then
        if p+2<l then
	  # move
	  HIDDEN_GVARS{[p..l-3]}:=HIDDEN_GVARS{[p+3..l]};
	fi;
	# remove
	Unbind(HIDDEN_GVARS[l-2]);
	Unbind(HIDDEN_GVARS[l-1]);
	Unbind(HIDDEN_GVARS[l]);
	l:=l-3;
	which:=Filtered(which,i->i<>str);
      fi;
    fi;
    p:=p-3;
  od;
  if all then 
    HIDDEN_GVARS:=[];
  fi;
end);



#############################################################################
##
#E  global.gi . . . . . . . . . . . . . . . . . . . . . . . . . . . ends here

