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32 injection

%--------------------------------------------------%
% vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
%--------------------------------------------------%
% Copyright (C) 2005-2006, 2010-2011 The University of Melbourne.
% This file may only be copied under the terms of the GNU Library General
% Public License - see the file COPYING.LIB in the Mercury distribution.
%--------------------------------------------------%
%
% File: injection.m.
% Author: mark.
% Stability: low.
%
% This module provides the `injection' ADT.  An injection is like a `map'
% (see map.m) but it allows efficient reverse lookups, similarly to `bimap'.
% This time efficiency comes at the expense of using twice as much space
% or more.  The difference between an injection and a bimap is that there
% can be values in the range of the injection that are not returned for any
% key, but for which a reverse lookup will still return a valid key.
%
% The invariants on this data structure, which are enforced by this module,
% are as follows:
%
% 1) For any key K, if a forward lookup succeeds with value V then a reverse
% lookup of value V will succeed with key K.
%
% 2) For any value V, if a reverse lookup succeeds with key K then a forward
% lookup of key K will succeed with some value (not necessarily V).
%
%--------------------------------------------------%
%--------------------------------------------------%

:- module injection.
:- interface.

:- import_module assoc_list.
:- import_module list.
:- import_module map.

%--------------------------------------------------%

:- type injection(K, V).

%--------------------------------------------------%

    % Initialize an empty injection.
    %
:- func init = injection(K, V).
:- pred init(injection(K, V)::out) is det.

    % Initialize an injection with the given key-value pair.
    %
:- func singleton(K, V) = injection(K, V).

    % Check whether an injection is empty.
    %
:- pred is_empty(injection(K, V)::in) is semidet.

    % Search the injection for the value corresponding to a given key.
    %
:- func forward_search(injection(K, V), K) = V is semidet.
:- pred forward_search(injection(K, V)::in, K::in, V::out)
    is semidet.

    % Search the injection for the key corresponding to a given value.
    %
:- func reverse_search(injection(K, V), V) = K is semidet.
:- pred reverse_search(injection(K, V)::in, K::out, V::in)
    is semidet.

    % Combined forward/reverse search.
    % (Declaratively equivalent to reverse_search.)
    %
:- pred search(injection(K, V), K, V).
:- mode search(in, in, out) is cc_nondet.
:- mode search(in, out, in) is semidet.

    % Look up the value for a given key, but throw an exception if it
    % is not present.
    %
:- func lookup(injection(K, V), K) = V.
:- pred lookup(injection(K, V)::in, K::in, V::out) is det.

    % Look up the key for a given value, but throw an exception if it
    % is not present.
    %
:- func reverse_lookup(injection(K, V), V) = K.
:- pred reverse_lookup(injection(K, V)::in, K::out, V::in) is det.

    % Return the list of all keys in the injection.
    %
:- func keys(injection(K, V)) = list(K).
:- pred keys(injection(K, V)::in, list(K)::out) is det.

    % Return the list of all values in the injection.
    %
:- func values(injection(K, V)) = list(V).
:- pred values(injection(K, V)::in, list(V)::out) is det.

    % Succeeds if the injection contains the given key.
    %
:- pred contains_key(injection(K, V)::in, K::in) is semidet.

    % Succeeds if the injection contains the given value.
    %
:- pred contains_value(injection(K, V)::in, V::in) is semidet.

    % Insert a new key-value pair into the injection.  Fails if either
    % the key or value already exists.
    %
:- func insert(injection(K, V), K, V) = injection(K, V) is semidet.
:- pred insert(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is semidet.

    % As above but throws an exception if the key or the value already
    % exists.
    %
:- func det_insert(injection(K, V), K, V) = injection(K, V).
:- pred det_insert(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is det.

    % Update the value associated with a given key.  Fails if the key
    % does not already exist, or if the value is already associated
    % with a key.
    %
:- func update(injection(K, V), K, V) = injection(K, V) is semidet.
:- pred update(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is semidet.

    % As above, but throws an exception if the key does not already exist,
    % or if the value is already associated with a key.
    %
:- func det_update(injection(K, V), K, V) = injection(K, V).
:- pred det_update(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is det.

    % Sets the value associated with a given key, regardless of whether
    % the key exists already or not.  Fails if the value is already
    % associated with a key that is different from the given key.
    %
:- func set(injection(K, V), K, V) = injection(K, V) is semidet.
:- pred set(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is semidet.

    % As above, but throws an exception if the value is already associated
    % with a key that is different from the given key.
    %
:- func det_set(injection(K, V), K, V) = injection(K, V).
:- pred det_set(injection(K, V)::in, K::in, V::in,
    injection(K, V)::out) is det.

    % Insert key-value pairs from an assoc_list into the given injection.
    % Fails if any of the individual inserts would fail.
    %
:- func insert_from_assoc_list(assoc_list(K, V), injection(K, V)) =
    injection(K, V) is semidet.
:- pred insert_from_assoc_list(assoc_list(K, V)::in,
    injection(K, V)::in, injection(K, V)::out) is semidet.

    % As above, but throws an exception if any of the individual
    % inserts would fail.
    %
:- func det_insert_from_assoc_list(assoc_list(K, V),
    injection(K, V)) = injection(K, V).
:- pred det_insert_from_assoc_list(assoc_list(K, V)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Set key-value pairs from an assoc_list into the given injection.
    % Fails of any of the individual sets would fail.
    %
:- func set_from_assoc_list(assoc_list(K, V), injection(K, V)) =
    injection(K, V) is semidet.
:- pred set_from_assoc_list(assoc_list(K, V)::in,
    injection(K, V)::in, injection(K, V)::out) is semidet.

    % As above, but throws an exception if any of the individual sets
    % would fail.
    %
:- func det_set_from_assoc_list(assoc_list(K, V), injection(K, V)) =
    injection(K, V).
:- pred det_set_from_assoc_list(assoc_list(K, V)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Insert key-value pairs from corresponding lists into the given
    % injection.  Fails if any of the individual inserts would fail.
    % Throws an exception if the lists are not of equal length.
    %
:- func insert_from_corresponding_lists(list(K), list(V),
    injection(K, V)) = injection(K, V) is semidet.
:- pred insert_from_corresponding_lists(list(K)::in, list(V)::in,
    injection(K, V)::in, injection(K, V)::out) is semidet.

    % As above, but throws an exception if any of the individual
    % inserts would fail.
    %
:- func det_insert_from_corresponding_lists(list(K), list(V),
    injection(K, V)) = injection(K, V).
:- pred det_insert_from_corresponding_lists(list(K)::in, list(V)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Set key-value pairs from corresponding lists into the given
    % injection.  Fails of any of the individual sets would fail.
    % Throws an exception if the lists are not of equal length.
    %
:- func set_from_corresponding_lists(list(K), list(V),
    injection(K, V)) = injection(K, V) is semidet.
:- pred set_from_corresponding_lists(list(K)::in, list(V)::in,
    injection(K, V)::in, injection(K, V)::out) is semidet.

    % As above, but throws an exception if any of the individual sets
    % would fail.
    %
:- func det_set_from_corresponding_lists(list(K), list(V),
    injection(K, V)) = injection(K, V).
:- pred det_set_from_corresponding_lists(list(K)::in, list(V)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Delete a key from an injection.  Also deletes any values that
    % correspond to that key.  If the key is not present, leave the
    % injection unchanged.
    %
:- func delete_key(injection(K, V), K) = injection(K, V).
:- pred delete_key(K::in, injection(K, V)::in, injection(K, V)::out) is det.

    % Delete a value from an injection.  Throws an exception if there is
    % a key that maps to this value.  If the value is not present, leave
    % the injection unchanged.
    %
:- func delete_value(injection(K, V), V) = injection(K, V).
:- pred delete_value(V::in, injection(K, V)::in, injection(K, V)::out) is det.

    % Apply delete_key to a list of keys.
    %
:- func delete_keys(injection(K, V), list(K)) = injection(K, V).
:- pred delete_keys(list(K)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Apply delete_value to a list of values.
    %
:- func delete_values(injection(K, V), list(V)) = injection(K, V).
:- pred delete_values(list(V)::in,
    injection(K, V)::in, injection(K, V)::out) is det.

    % Merge the contents of the two injections.  Both sets of keys must
    % be disjoint, and both sets of values must be disjoint.
    %
:- func merge(injection(K, V), injection(K, V)) = injection(K, V).
:- pred merge(injection(K, V)::in, injection(K, V)::in, injection(K, V)::out)
    is det.

    % Merge the contents of the two injections.  For keys that occur in
    % both injections, map them to the value in the second argument.
    % Both sets of values must be disjoint.
    %
:- func overlay(injection(K, V), injection(K, V)) = injection(K, V).
:- pred overlay(injection(K, V)::in, injection(K, V)::in, injection(K, V)::out)
    is det.

    % Apply an injection to a list of keys.
    % Throws an exception if any of the keys are not present.
    %
:- func apply_forward_map_to_list(injection(K, V), list(K)) = list(V).
:- pred apply_forward_map_to_list(injection(K, V)::in, list(K)::in,
    list(V)::out) is det.

    % Apply the inverse of an injection to a list of values.
    % Throws an exception if any of the values are not present.
    %
:- func apply_reverse_map_to_list(injection(K, V), list(V)) = list(K).
:- pred apply_reverse_map_to_list(injection(K, V)::in, list(V)::in,
    list(K)::out) is det.

    % Apply a transformation to all the keys in the injection.  If two
    % distinct keys become equal under this transformation then the
    % value associated with the greater of these two keys is used in the
    % result.
    %
:- func map_keys(func(V, K) = L, injection(K, V)) = injection(L, V).
:- pred map_keys(pred(V, K, L)::in(pred(in, in, out) is det),
    injection(K, V)::in, injection(L, V)::out) is det.

    % Same as map_keys, but deletes any keys for which the
    % transformation fails.
    %
:- pred filter_map_keys(pred(V, K, L)::in(pred(in, in, out) is semidet),
    injection(K, V)::in, injection(L, V)::out) is det.

    % Apply a transformation to all the values in the injection.  If two
    % distinct values become equal under this transformation then the
    % reverse search of these two values in the original map must lead
    % to the same key.  If it doesn't, then throw an exception.
    %
:- func map_values(func(K, V) = W, injection(K, V)) = injection(K, W).
:- pred map_values(pred(K, V, W)::in(pred(in, in, out) is det),
    injection(K, V)::in, injection(K, W)::out) is det.

    % Extract the forward map from an injection.
    %
:- func forward_map(injection(K, V)) = map(K, V).
:- pred forward_map(injection(K, V)::in, map(K, V)::out) is det.

    % Extract the reverse map from an injection.
    %
:- func reverse_map(injection(K, V)) = map(V, K).
:- pred reverse_map(injection(K, V)::in, map(V, K)::out) is det.

%--------------------------------------------------%
%--------------------------------------------------%


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