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%-----------------------------------------------------------------------------%
% Copyright (C) 1997, 1999 The University of Melbourne.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%-----------------------------------------------------------------------------%
%
% inst.m - Contains the (inst) data type.
% Main author: bromage
%
%-----------------------------------------------------------------------------%
:- module (inst).
:- interface.
% This module should NOT import hlds*.m. Any types which are needed in
% both the insts and in the HLDS should be defined here, rather than
% in hlds*.m, because insts are part of the parse tree and the parse tree
% should not depend on the HLDS.
%
% XXX Currently we have to import hlds_data for the `cons_id' type.
% I think the cons_ids in insts only use a subset of the functors
% of the `cons_id' type, and so we could define a new type
% `abstract_cons_id' and use that here instead of `cons_id'.
:- import_module prog_data, hlds_data.
:- import_module list, std_util.
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
:- type (inst)
---> any(uniqueness)
; free
; free(type)
; bound(uniqueness, list(bound_inst))
% The list(bound_inst) must be sorted
; ground(uniqueness, maybe(pred_inst_info))
% The pred_inst_info is used for
% higher-order pred modes
; not_reached
; inst_var(inst_var)
% A defined_inst is possibly recursive
% inst whose value is stored in the
% inst_table. This is used both for
% user-defined insts and for
% compiler-generated insts.
; defined_inst(inst_name)
% An abstract inst is a defined inst which
% has been declared but not actually been
% defined (yet).
; abstract_inst(sym_name, list(inst)).
:- type uniqueness
---> shared % there might be other references
; unique % there is only one reference
; mostly_unique % there is only one reference
% but there might be more on
% backtracking
; clobbered % this was the only reference, but
% the data has already been reused
; mostly_clobbered.
% this was the only reference, but
% the data has already been reused;
% however, there may be more references
% on backtracking, so we will need to
% restore the old value on backtracking
% higher-order predicate terms are given the inst
% `ground(shared, yes(PredInstInfo))'
% where the PredInstInfo contains the extra modes and the determinism
% for the predicate. Note that the higher-order predicate term
% itself must be ground.
:- type pred_inst_info
---> pred_inst_info(
pred_or_func, % is this a higher-order func
% mode or a higher-order pred
% mode?
list(mode), % the modes of the additional
% (i.e. not-yet-supplied)
% arguments of the pred;
% for a function, this includes
% the mode of the return value
% as the last element of the
% list.
determinism % the determinism of the
% predicate or function
).
:- type bound_inst ---> functor(cons_id, list(inst)).
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
:- implementation.
% Empty for now.
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
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