=pod

=encoding utf8

=head1 NAME

Muldis::D::Ext::Set -
Muldis D extension for Set and Maybe specific operators

=head1 VERSION

This document is Muldis::D::Ext::Set version 0.91.0.

=head1 PREFACE

This document is part of the Muldis D language specification, whose root
document is L<Muldis::D>; you should read that root document
before you read this one, which provides subservient details.

=head1 DESCRIPTION

Muldis D has a mandatory core set of system-defined (eternally available)
entities, which is referred to as the I<Muldis D core> or the I<core>; they
are the minimal entities that all Muldis D implementations need to provide;
they are mutually self-describing and are used to bootstrap the language;
any entities outside the core, called I<Muldis D extensions>, are
non-mandatory and are defined in terms of the core or each other, but the
reverse isn't true.

This current C<Set> document describes the system-defined I<Muldis D Set
Extension>, which consists of generic operators that are specific to the
C<Set> and C<Maybe> parameterized relation types, and said operators
are short-hands for generic relational operators in the language core.

This current document does not describe the polymorphic operators that all
types, or some types including core types, have defined over them; said
operators are defined once for all types in L<Muldis::D::Core>.

I<This documentation is pending.>

=head1 SYSTEM-DEFINED SET-CONCERNING FUNCTIONS

=head2 sys.std.Set.has_member

C<< function sys.std.Set.has_member (Bool <-- Set $set, Universal $value)
>>

This function results in C<Bool:true> iff its C<value> argument matches the
sole attribute of a tuple of its C<set> argument (that is, iff
conceptually C<value> is a member of C<set>), and C<Bool:false> otherwise.
This function will warn if its 2 arguments are incompatible as per
C<sys.std.Core.Relation.is_subset>.  Note that this operation is also known
as C<S∋>.

=head2 sys.std.Set.has_not_member

C<< function sys.std.Set.has_not_member (Bool <-- Set $set,
Universal $value) >>

This function is exactly the same as C<sys.std.Set.has_member> except that
it results in the opposite boolean value when given the same arguments.
Note that this operation is also known as C<S∌>.

=head2 sys.std.Set.value_is_member

C<< function sys.std.Set.value_is_member (Bool <--
Universal $value, Set $set) >>

This function is an alias for C<sys.std.Set.has_member>.  This function
results in C<Bool:true> iff its C<value> argument matches the
sole attribute of a tuple of its C<set> argument (that is, iff
conceptually C<value> is a member of C<set>), and C<Bool:false>
otherwise.  Note that this operation is also known as C<S∈>.

=head2 sys.std.Set.value_is_not_member

C<< function sys.std.Set.value_is_not_member (Bool <--
Universal $value, Set $set) >>

This function is an alias for C<sys.std.Set.has_not_member>.  This function
is exactly the same as C<sys.std.Set.value_is_member> except that it
results in the opposite boolean value when given the same arguments.  Note
that this operation is also known as C<S∉>.

=head2 sys.std.Set.insertion

C<< function sys.std.Set.insertion (Set <-- Set $set, Universal $value) >>

This function results in a C<Set> that is the relational union of C<set>
and a Set whose sole tuple has the sole attribute value of C<value>;
that is, conceptually the result is C<value> inserted into C<set>.  As a
trivial case, if C<value> already exists in C<set>, then the result is just
C<set>.

=head2 sys.std.Set.disjoint_ins

C<< function sys.std.Set.disjoint_ins (Set <-- Set $set,
Universal $value) >>

This function is exactly the same as C<sys.std.Set.insertion> except that
it will fail if C<value> already exists in C<set>.

=head2 sys.std.Set.deletion

C<< function sys.std.Set.deletion (Set <-- Set $set, Universal $value) >>

This function results in a C<Set> that is the relational difference from
C<set> of a Set whose sole tuple has the sole attribute value of
C<value>; that is, conceptually the result is C<value> deleted from C<set>.
As a trivial case, if C<value> already doesn't exist in C<set>, then the
result is just C<set>.

=head2 sys.std.Set.reduction

C<< function sys.std.Set.reduction (Universal <-- Set $topic,
ValRedFuncRef $func, Universal $identity) >>

This function is a generic reduction operator that recursively takes each
pair of input values in C<topic> and applies an argument-specified scalar
or nonscalar value-resulting C<value_reduction> function (which is both
commutative and associative) to the pair until just one input value is
left, which is the result.  The C<value_reduction> function to apply is
named in the C<func> argument, and that
function must have 2 parameters named C<v1> and C<v2>, which take
the 2 input scalar or nonscalar values for an
invocation.  If C<topic> has zero values, then C<reduction> results in the
value given in C<identity>.  I<Note that C<identity> may be changed to take
a function name rather than a value, for consistency with C<func>.>  This
function will fail|warn if the |declared type of C<identity> isn't a
subtype of the |declared type of the sole attribute of C<topic>.

=head2 sys.std.Set.maybe_reduction

C<< function sys.std.Set.maybe_reduction (Maybe <-- Set $topic,
ValRedFuncRef $func) >>

This function is exactly the same as C<sys.std.Set.reduction> except that
it does not take an C<identity> argument, and it results in a C<Maybe> of
what is otherwise the result type, and that result has zero elements if the
argument has zero elements.

=head2 sys.std.Set.Set_from_wrap

C<< function sys.std.Set.Set_from_wrap (set_of.Tuple <--
Relation $topic) >>

This function results in a C<Set> whose sole attribute is tuple-typed
and the attribute values are all the tuples of C<topic>; is a short-hand
for a relational wrap of all attributes of C<topic> such that the new
tuple-valued attribute is named C<value>.

=head2 sys.std.Set.Set_from_attr

C<< function sys.std.Set.Set_from_attr (Set <-- Relation $topic,
Name $name) >>

This function results in a C<Set> consisting of all the values of the
attribute of C<topic> named by C<name>.  It is a short-hand for a unary
projection of just the named attribute plus its renaming to C<value>.

=head1 SYSTEM-DEFINED MAYBE-CONCERNING FUNCTIONS

=head2 sys.std.Set.Maybe.nothing

C<< function sys.std.Set.Maybe.nothing (Maybe <--) >>

This C<named_value> selector function results in the only zero-tuple Maybe
value, which is known by the special name C<Maybe:nothing>, aka C<nothing>,
aka I<empty set> aka C<∅>.

=head2 sys.std.Set.Maybe.single

C<< function sys.std.Set.Maybe.single (Single <-- Universal $value) >>

This selector function results in the Maybe value with a single tuple
whose C<value> attribute's value is the C<value> argument.  Note that this
operation is also known as C<s>.

=head2 sys.std.Set.Maybe.attr

C<< function sys.std.Set.Maybe.attr (Universal <-- Single $topic) >>

This function results in the scalar or nonscalar value of the sole
attribute of the sole tuple of its argument, which always exists when the
argument is a C<Single>.  Note that this operation is also known as C<v>.

=head2 sys.std.Set.Maybe.attr_or_default

C<< function sys.std.Set.Maybe.attr_or_default (Universal <--
array_of.Maybe $topic?, TypeRef $default) >>

This function results in the scalar or nonscalar value of the sole
attribute of the sole tuple of the lowest-indexed of its N C<topic> input
element values where said element isn't equal to C<nothing>, if there is
such an element; otherwise, it results in the default value of the scalar
or nonscalar data type whose name is given in the C<default> argument.
This function is a short-hand for invoking C<attr_or_value> with the result
from invoking C<sys.std.Core.Universal.default>.  Note that this operation
is also known as C<//d>.

=head2 sys.std.Set.Maybe.attr_or_value

C<< function sys.std.Set.Maybe.attr_or_value (Universal <--
array_of.Maybe $topic?, Universal $value) >>

This function results in the scalar or nonscalar value of the sole
attribute of the sole tuple of the lowest-indexed of its N C<topic> input
element values where said element isn't equal to C<nothing>, if there is
such an element, and otherwise it results in C<value>.  This function will
warn if the declared type of C<value> isn't a subtype of the declared type
of the attribute.  Note that this operation is also known as C<//>.  In
situations where a C<Maybe> is used analagously to a SQL nullable value,
this function is analagous to the N-adic SQL COALESCE function.

=head2 sys.std.Set.Maybe.order

C<< function sys.std.Set.Maybe.order (Order <-- Maybe $topic,
Maybe $other, Bool $treat_nothing_as_max, OrdDetFuncRef $ord_func?,
Bool $reverse_order_of_singles?) >>

This function is a generic (total) C<order_determination> function for
C<Maybe> values.  Iff both of its C<topic> and C<other> arguments are
identical, this function results in C<Order:same>.  Otherwise, iff both of
those 2 arguments are C<Single> values, then the result of this function
is the result of applying to those 2 arguments the (total)
C<order_determination> function given in its C<ord_func> argument, as
curried by its C<reverse_order_of_singles> argument.
Otherwise, iff C<topic> is C<nothing>, this function results in
C<Order:increase> or C<Order:decrease> respectively when
C<treat_nothing_as_max> is C<Bool:false> (the default) or C<Bool:true>.
Otherwise (iff C<other> is C<nothing>), this function results in the
reverse of when only C<topic> is C<nothing>.  In situations where a
C<Maybe> is used analagously to a SQL nullable value and this function is
analagous to the dyadic comparison underlying a SQL "ORDER BY", then
C<reverse_order_of_singles> designates SQL's "ASC|DESC" and
C<treat_nothing_as_max> designates SQL's "NULLS FIRST|LAST".

=head1 SEE ALSO

Go to L<Muldis::D> for the majority of distribution-internal
references, and L<Muldis::D::SeeAlso> for the majority of
distribution-external references.

=head1 AUTHOR

Darren Duncan (C<perl@DarrenDuncan.net>)

=head1 LICENSE AND COPYRIGHT

This file is part of the formal specification of the Muldis D language.

Muldis D is Copyright © 2002-2009, Muldis Data Systems, Inc.

See the LICENSE AND COPYRIGHT of L<Muldis::D> for details.

=head1 TRADEMARK POLICY

The TRADEMARK POLICY in L<Muldis::D> applies to this file too.

=head1 ACKNOWLEDGEMENTS

The ACKNOWLEDGEMENTS in L<Muldis::D> apply to this file too.

=cut
