spec for #3662 and #3609

typechecker/en/modules/expressions.xml

@@ -1419,31 +1419,72 @@ Digit{1,2} ":" Digit{2} ( ":" Digit{2} ( ":" Digit{3} )? )?
 
  <section id="inlineconditionalexpressions">
  <title>Inline conditional expressions</title>
-
- <comment>
- <para>We plan to support inline <literal>if/then/else</literal> conditional 
- expressions, for example:</para>
- <programlisting>Integer port = if (exists setting = process.propertyValue("port")) 
- then parseInteger(setting) else 8080;</programlisting>
- <para>Note that this is more powerful than the <literal>then</literal> and
- <literal>else</literal> operators because it allows all kinds of conditions,
- not only boolean conditions.</para>
- <para>Should we also support:</para>
+
+ <para>A conditional expression comes in two forms:</para>
+
  <itemizedlist>
  <listitem>
- <para>inline <literal>switch/case/else</literal> conditional 
- expressions, or even</para>
+ <para>an <literal>if/then/else</literal> expression resembles 
+ the <literal>if/else</literal> conditional defined in 
+ <xref linkend="ifelse"/>, and</para>
  </listitem>
  <listitem>
- <para>inline <literal>try/catch</literal> exceptional conditions?</para>
+ <para>a <literal>switch/case/else</literal> expression resembles 
+ the <literal>switch/case/else</literal> conditional defined in 
+ <xref linkend="switchcaseelse"/>.</para>
+ </listitem>
+ </itemizedlist>
+
+ <synopsis>ConditionalExpression: IfElseExpression | SwitchCaseElseExpression</synopsis>
+
+ <para>An <literal>if/then/else</literal> expression has a condition 
+ list, as defined in <xref linkend="controlstructureconditions"/>, a
+ <literal>then</literal> expression, and an <literal>else</literal> 
+ expression. The <literal>else</literal> expression is not optional.</para>
+
+ <synopsis>IfElseExpression: "if" ConditionList ThenExpression ElseExpression</synopsis>
+
+ <para>The type of an <literal>if/then/else</literal> expression with
+ <literal>then</literal> expression of type <literal>X</literal> and
+ <literal>else</literal> expression of type <literal>Y</literal> is
+ <literal>X|Y</literal>.</para>
+
+ <para>A <literal>switch/case/else</literal> expression has a 
+ <literal>switch</literal> expression, a list of <literal>case</literal>
+ expressions, and, optionally, an <literal>else</literal> expression.</para>
+
+ <synopsis>SwitchCaseElseExpression: "switch" "(" Expression ")" CaseExpression ElseExpression</synopsis>
+
+ <para>The type of an <literal>if/then/else</literal> expression with
+ <literal>case</literal> expressions of type <literal>X1</literal>,
+ <literal>X2</literal>, ..., <literal>Xn</literal> and
+ <literal>else</literal> expression of type <literal>Y</literal> is
+ <literal>X1|X2|...|Xn|Y</literal>.</para>
+
+ <synopsis>ThenExpression: "then" Expression</synopsis>
+ <synopsis>ElseExpression: "else" Expression</synopsis>
+ <synopsis>CaseExpression: "case" "(" Case ")" Expression</synopsis>
+
+ <para>The expression following <literal>then</literal>, 
+ <literal>else</literal>, and <literal>case</literal> is parsed with 
+ precedence just higher than the <literal>||</literal> operator, and 
+ just lower than the <literal>then</literal> and <literal>else</literal> 
+ operators, that is, between the layers 3 and 4 defined in
+ <xref linkend="operatorprecedence"/>.</para>
+
+ <para>Each <literal>case</literal> expression includes a value case or
+ type case, as defined in <xref linkend="switchcaseelse"/>. Just like
+ in a <literal>switch/case/else</literal> conditional statement:</para>
+
+ <itemizedlist>
+ <listitem>
+ <para>all cases must be disjoint, and</para>
+ </listitem>
+ <listitem>
+ <para>if there is no <literal>else</literal> expression,
+ the cases must be exhaustive.</para>
  </listitem>
  </itemizedlist>
- <para>For example:</para>
- <programlisting>Float evaluated => switch (expr)
- case (is Literal) expr.integer
- case (is Plus) expr.left.evaluated + expr.right.evaluated
- case (is Times) expr.left.evaluated * expr.right.evaluated;</programlisting>
- </comment>
 
  </section>