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% vim: ft=mercury ts=4 sw=4 et
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% Copyright (C) 2002-2009, 2011 The University of Melbourne.
% Copyright (C) 2014-2021 The Mercury team.
% This file is distributed under the terms specified in COPYING.LIB.
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%
% File: construct.m.
% Main author: zs.
% Stability: low.
%
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:- module construct.
:- interface.

:- import_module list.
:- import_module maybe.
:- import_module univ.
:- import_module type_desc.

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    % The functors of a discriminated union type are numbered from
    % zero to N-1, where N is the value returned by num_functors.
    % The functors are numbered in lexicographic order. If two
    % functors have the same name, the one with the lower arity
    % will have the lower number.
    %
:- type functor_number_ordinal == int.
:- type functor_number_lex == int.

    % num_functors(Type).
    %
    % Returns the number of different functors for the top-level
    % type constructor of the type specified by Type.
    % Fails if the type is not a discriminated union type.
    %
    % deconstruct.functor_number/3, deconstruct.deconstruct_du/5
    % and the semidet predicates and functions in this module will
    % only succeed for types for which num_functors/1 succeeds.
    %
:- func num_functors(type_desc) = int is semidet.

:- func det_num_functors(type_desc) = int.

    % get_functor(Type, FunctorNumber, FunctorName, Arity, ArgTypes).
    %
    % Binds FunctorName and Arity to the name and arity of functor number
    % FunctorNumber for the specified type, and binds ArgTypes to the
    % type_descs for the types of the arguments of that functor.
    % Fails if the type is not a discriminated union type, or if
    % FunctorNumber is out of range.
    %
:- pred get_functor(type_desc::in, functor_number_lex::in,
    string::out, int::out, list(pseudo_type_desc)::out) is semidet.

    % get_functor_with_names(Type, FunctorNumber, FunctorName, Arity, ArgTypes,
    %   ArgNames).
    %
    % Binds FunctorName and Arity to the name and arity of functor number
    % FunctorNumber for the specified type, ArgTypes to the type_descs
    % for the types of the arguments of that functor, and ArgNames to the
    % field name of each functor argument, if any. Fails if the type is
    % not a discriminated union type, or if FunctorNumber is out of range.
    %
:- pred get_functor_with_names(type_desc::in, functor_number_lex::in,
    string::out, int::out, list(pseudo_type_desc)::out,
    list(maybe(string))::out) is semidet.

    % get_functor_ordinal(Type, I) = Ordinal.
    %
    % Returns Ordinal, where Ordinal is the position in declaration order
    % for the specified type of the function symbol that is in position I
    % in lexicographic order. Fails if the type is not a discriminated
    % union type, or if I is out of range.
    %
:- func get_functor_ordinal(type_desc, functor_number_lex) =
    functor_number_ordinal is semidet.
:- pred get_functor_ordinal(type_desc::in, functor_number_lex::in,
    functor_number_ordinal::out) is semidet.

    % get_functor_lex(Type, Ordinal) = I.
    %
    % Returns I, where I is the position in lexicographic order for the
    % specified type of the function symbol that is in position Ordinal
    % in declaration order. Fails if the type is not a discriminated
    % union type, or if Ordinal is out of range.
    %
:- func get_functor_lex(type_desc, functor_number_ordinal) =
    functor_number_lex is semidet.

    % find_functor(Type, FunctorName, Arity, FunctorNumber, ArgTypes).
    %
    % Given a type descriptor, a functor name and arity, finds the functor
    % number and the types of its arguments. It thus serves as the converse
    % to get_functor/5.
    %
:- pred find_functor(type_desc::in, string::in, int::in,
    functor_number_lex::out, list(type_desc)::out) is semidet.

    % construct(Type, I, Args) = Term.
    %
    % Returns a term of the type specified by Type whose functor
    % is functor number I of the type given by Type, and whose
    % arguments are given by Args. Fails if the type is not a
    % discriminated union type, or if I is out of range, or if the
    % number of arguments supplied doesn't match the arity of the selected
    % functor, or if the types of the arguments do not match
    % the expected argument types of that functor.
    %
:- func construct(type_desc, functor_number_lex, list(univ)) = univ is semidet.

    % construct_tuple(Args) = Term.
    %
    % Returns a tuple whose arguments are given by Args.
    %
:- func construct_tuple(list(univ)) = univ.

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