<?xml version="1.0"?>
<!--
  Copyright (C) 2014-2023 Ryan Specialty, LLC.

  This file is part of tame-core.

  tame-core is free software: you can redistribute it and/or modify it
  under the terms of the GNU General Public License as
  published by the Free Software Foundation, either version 3 of the
  License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-->
<package xmlns="http://www.lovullo.com/rater"
         xmlns:c="http://www.lovullo.com/calc"
         xmlns:t="http://www.lovullo.com/rater/apply-template"
         core="true"
         desc="Base features">

  The \pkgself~package exposes common and internal
  defintions.  Ideally, this package will be included automatically by
  the compiler to remove repetitive, boilerplate imports.  Importing
  this package isn't necessary if none of these definitions are
  needed.



  <section title="Internal Constants">
    \ref{_CMATCH_} is a magic constant that contains the result of
    a~classification match.  This is used implicity by
    \ref{rate-each}.\footnote{The symbol is \Xi~because it looks like
    a sideways array.}

    \todo{Remove in favor of a local variable or generated
    classification; there is no need (anymore) for this to be magic.}

    <const name="_CMATCH_" type="boolean" sym="\Xi"
           desc="Classification match vector (applicability)">
      <item value="0"
            desc="Dummy value; this set is populated upon entering
                  each rate block" />
    </const>
  </section>



  <section title="Primitive Types">
    Primitives are defined internally; these definitions simply
    provide symbols to permit their use.

    <typedef name="integer"
             desc="Any value in the set of integers"
             sym="\mathbb{I}">
      <base-type />
    </typedef>


    <typedef name="float"
             desc="Any real number (represented as a float)"
             sym="\mathbb{R}">
      <base-type />
    </typedef>


    \ref{empty} does not have much use outside of the compiler.

    <typedef name="empty"
             desc="Empty set"
             sym="\emptyset">
      <base-type />
    </typedef>
  </section>


  <section title="Boolean and Unknown">
    \ref{boolean} contains the boolean \ref{TRUE} and~\ref{FALSE} values,
      which map to~$1$ and~$0$ respectively.
    The \ref{maybe} type is the union of \ref{boolean} and \ref{NOTHING},
      with a value of~$-1$;\footnote{
          This is similar in spirit to the Haskell \tt{Maybe} type,
            or the OCaml \tt{Option} type.
        }this is commonly used to represent an unknown state or missing
        value.\footnote{
          The \ref{nothing}~type is used for the sake of the union;
            it should not be used directly.}

    <typedef name="maybe" desc="Boolean or unknown value">
      <union>
        <typedef name="nothing" desc="Unknown value">
          <enum type="integer">
            <item name="NOTHING" value="-1" desc="Unknown or missing value" />
          </enum>
        </typedef>

        <typedef name="boolean" desc="Boolean values">
          <enum type="integer">
            <item name="TRUE"  value="1" desc="True" />
            <item name="FALSE" value="0" desc="False" />
          </enum>
        </typedef>
      </union>
    </typedef>

    The constant \ref{UNKNOWN} is also defined as~$-1$ to serve as an
      alternative to the term~``nothing''.

    <const name="UNKNOWN" value="-1"
           desc="Unknown or missing value" />
  </section>



  <section title="Convenience">
    $0$~is a~common value.  Where a value is required (such
    as a~template argument), \ref{ZERO} may be used.  TAME now
    supports a~constant-scalar syntax ({\tt #0}; \todo{reference this
    in documentation}), making this largely unnecessary.

    This is declared as a float to provide compatibility with all
    types of expressions.

    <const name="ZERO" value="0.00"
           desc="Zero value" />


    In the case where classifications are required, but a~static
    assumption about the applicability of the subject can be made, we
    have values that are always~true and always~false.  The use
    of~\ref{never} may very well be a~code smell, but let us not rush
    to judgment.\footnote{\ref{never} has been added as an analog
    to~\ref{always}; its author has never had use for it.  Oh, look,
    we just used ``never''.}

    <classify as="always"
              desc="Always true"
              yields="alwaysTrue" />

    <classify as="never"
              any="true"
              desc="Never true"
              yields="neverTrue" />
  </section>



  <section title="Work-In-Progress">
    \ref{_todo_} formalizes TODO items and may optionally yield a
      value~\tt{@value@} for use within calculations.%
        \footnote{This is different than its previous behavior of always
                    yielding a scalar~$0$.}
    All uses of the \ref{_todo_} template will produce a warning composed of
      its description~\tt{@desc@}.

    <template name="_todo_"
              desc="Represents work that needs to be done">
      <param name="@desc@" desc="TODO desc">
        <text>TODO</text>
      </param>

      <param name="@value@" desc="Placeholder value" />
      <param name="@index@" desc="Placeholder value index">
        <text></text>
      </param>

      <unless name="@value@">
        <unless name="@index@" eq="">
          <error>Using @index@ without @value@</error>
        </unless>
      </unless>


      <warning>
        TODO: <param-value name="@desc@" />
      </warning>


      <if name="@value@">
        <c:value-of name="@value@" index="@index@" />
      </if>
    </template>


    The \ref{_ignore_} template serves as a~block
    comment.\footnote{This is useful since XML does not support nested
    comments, which makes it difficult to comment out code that
    already has XML comments.}  It may be useful for debugging, but is
    discouraged for use otherwise.  The \ref{_ignore_/@desc@} param
    should be used to describe intent.

    <template name="_ignore_"
              desc="Removes all child nodes (as if commented out)">
      <param name="@values@" desc="Nodes to comment out" />
      <param name="@desc@"   desc="Reason for ignore" />


      <warning>Ignored block!</warning>
    </template>
  </section>


  <section title="Calculations">
    These templates represent calculations that used to be defined as XSLT
      templates before TAME's template system existed.

    <extern name="___yield" type="rate" dtype="float" dim="0" />

    <template name="_yield_"
              desc="Final scalar result provided to caller">
      <param name="@values@" desc="Yield calculation" />

      <rate yields="___yield" local="true">
        <param-copy name="@values@" />
      </rate>
    </template>


    <template name="_rate-each_"
              desc="Convenience template that expands to a lv:rate block summing over
                    the magic _CMATCH_ set with the product of its value">
      <param name="@values@"
             desc="Yield calculation" />

      <param name="@generates@" desc="Generator name (optional)">
        <text></text>
      </param>

      <param name="@yields@" desc="Yield (optional)">
        <text>_</text>
        <param-value name="@generates@" />
      </param>

      <!-- at least one of generates or yields is required -->
      <if name="@yields@" eq="">
        <if name="@generates@" eq="">
          <error>must provide at least one of @generates or @yields</error>
        </if>
      </if>

      <param name="@class@"
             desc="Space-delimited classifications for predicated iteration" />
      <param name="@no@"
             desc="Space-delimited classifications for predicated iteration to prevent matches">
        <text></text>
      </param>

      <param name="@index@"
             desc="Generator index" />

      <param name="@dim@" desc="Dim (optional)">
        <text></text>
      </param>

      <param name="@gensym@" desc="Generator TeX symbol">
        <text></text>
      </param>

      <rate class="@class@" no="@no@" yields="@yields@"
            gentle-no="true"
            desc="Total {@yields@} premium">
        <c:sum of="_CMATCH_" dim="@dim@" sym="@gensym@"
               generates="@generates@" index="@index@"
               desc="Set of individual {@yields@} premiums">
          <c:product>
            <c:value-of name="_CMATCH_" index="@index@"
                        label="One if {@class@} and not {@no@} (if provided), otherwise zero" />
            <param-copy name="@values@" />
          </c:product>
        </c:sum>
      </rate>
    </template>
  </section>


  <section title="Feature Flags">
    These templates alter the behavior of the TAME compiler or runtime.
    They will be removed at some point in the future.


    <section title="Classification System">
      The template \tt{_use-new-classification-system_} sets a compile-time
        flag that will cause all following sibling classifications to be
        compiled using the new classification system.
      Once the feature is enabled by default,
        this template will become a noop and will begin to emit a warning,
          before eventually being removed.

      It is possible to mix both old and new classifications within the same
        package,
          though such behavior may lead to confusion in certain cases.
      For more information on where the new and old system differ,
        see the \tt{core/test/core/class} specification.

      <template name="_use-new-classification-system_"
                desc="Compile following-sibling::lv:classify using the new
                      classification system">
        <!-- Even though this is a template param-meta, it will only affect
             following-sibling for performance reasons -->
        <param-meta name="___feature-newclassify" value="1" />

        <t:todo desc="remove _use-new-classification-system_ application;
                      the new classification system is enabled by default
                      and this template no longer has any effect" />
      </template>
    </section>
  </section>
</package>

