Grammar changes for ceylon/ceylon-spec#869 – comprehensions beginning with if clause

changes.diff

diff --git a/Ceylon.g b/Ceylon.g
index 1ef1226..3dee8ef 100644
--- a/Ceylon.g
+++ b/Ceylon.g
@@ -1848,7 +1848,9 @@ anonymousFunction returns [Expression expression]
 comprehension returns [Comprehension comprehension]
     @init { $comprehension = new Comprehension(null); }
     : forComprehensionClause
-      { $comprehension.setForComprehensionClause($forComprehensionClause.comprehensionClause); }
+      { $comprehension.setInitialComprehensionClause($forComprehensionClause.comprehensionClause); }
+    | ifComprehensionClause
+      { $comprehension.setInitialComprehensionClause($ifComprehensionClause.comprehensionClause); }
     ;
 
 comprehensionClause returns [ComprehensionClause comprehensionClause]
diff --git a/Ceylon.nodes b/Ceylon.nodes
index f1101ec..761729d 100644
--- a/Ceylon.nodes
+++ b/Ceylon.nodes
@@ -823,7 +823,7 @@
 
 "A comprehension."
 ^(COMPREHENSION:POSITIONAL_ARGUMENT
-    FOR_COMPREHENSION_CLAUSE)
+    INITIAL_COMPREHENSION_CLAUSE)
 
 "A single clause of comprehension"
 ^(abstract COMPREHENSION_CLAUSE:CONTROL_CLAUSE
@@ -831,16 +831,19 @@
     ProducedType firstTypeModel;
     boolean possiblyEmpty;)
 
+"A clause that can appear at the beginning of a comprehension."
+^(abstract INITIAL_COMPREHENSION_CLAUSE:COMPREHENSION_CLAUSE)
+
 "The expression at the end of a comprehension."
 ^(EXPRESSION_COMPREHENSION_CLAUSE:COMPREHENSION_CLAUSE
     EXPRESSION)
 
 "A quantifier clause in a comprehension."
-^(FOR_COMPREHENSION_CLAUSE:COMPREHENSION_CLAUSE
+^(FOR_COMPREHENSION_CLAUSE:INITIAL_COMPREHENSION_CLAUSE
     FOR_ITERATOR
     COMPREHENSION_CLAUSE)
 
 "A filter clause in a comprehension."
-^(IF_COMPREHENSION_CLAUSE:COMPREHENSION_CLAUSE
+^(IF_COMPREHENSION_CLAUSE:INITIAL_COMPREHENSION_CLAUSE
     CONDITION_LIST
     COMPREHENSION_CLAUSE)
diff --git a/en/modules/expressions.xml b/en/modules/expressions.xml
index 77bde28..31c3360 100644
--- a/en/modules/expressions.xml
+++ b/en/modules/expressions.xml
@@ -858,13 +858,14 @@ Digit{1,2} ":" Digit{2} ( ":" Digit{2} ( ":" Digit{3} )? )?
                 </listitem>
             </itemizedlist>
             
-            <para>Every comprehension begins with a <literal>for</literal> clause, and 
-            ends with an expression clause. There may be any number of intervening 
+            <para>Every comprehension begins with a <literal>for</literal> or <literal>if</literal>
+            clause, and ends with an expression clause. There may be any number of intervening 
             <literal>for</literal> or <literal>if</literal> clauses. Each clause in the
             comprehension is considered a child of the clause that immediately precedes 
             it.</para>
             
-            <synopsis>Comprehension: ForComprehensionClause</synopsis>
+            <synopsis>Comprehension: InitialComprehensionClause</synopsis>
+            <synopsis>InitialComprehensionClause: ForComprehensionClause | IfComprehensionClause</synopsis>
             <synopsis>ForComprehensionClause: "for" ForIterator ComprehensionClause</synopsis>
             <synopsis>IfComprehensionClause: "if" ConditionList ComprehensionClause</synopsis>
             <synopsis>ComprehensionClause: ForComprehensionClause | IfComprehensionClause | Expression</synopsis>
diff --git a/src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java b/src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java
index b93bdfe..eca37fc 100644
--- a/src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java
+++ b/src/com/redhat/ceylon/compiler/typechecker/analyzer/ExpressionVisitor.java
@@ -2755,8 +2755,8 @@ public class ExpressionVisitor extends Visitor {
     
     private void checkComprehensionIndirectArgument(Tree.Comprehension c, 
             ProducedType paramType, boolean atLeastOne) {
-        Tree.ForComprehensionClause fcc = ((Tree.Comprehension) c).getForComprehensionClause();
-        if (fcc.getPossiblyEmpty() && atLeastOne) {
+        Tree.InitialComprehensionClause icc = ((Tree.Comprehension) c).getInitialComprehensionClause();
+        if (icc.getPossiblyEmpty() && atLeastOne) {
             c.addError("variadic parameter is required but comprehension is possibly empty");
         }
         ProducedType at = c.getTypeModel();
@@ -2802,8 +2802,8 @@ public class ExpressionVisitor extends Visitor {
     
     private void checkComprehensionPositionalArgument(Parameter p, ProducedReference pr,
             Tree.Comprehension c, boolean atLeastOne) {
-        Tree.ForComprehensionClause fcc = ((Tree.Comprehension) c).getForComprehensionClause();
-        if (fcc.getPossiblyEmpty() && atLeastOne) {
+        Tree.InitialComprehensionClause icc = ((Tree.Comprehension) c).getInitialComprehensionClause();
+        if (icc.getPossiblyEmpty() && atLeastOne) {
             c.addError("variadic parameter is required but comprehension is possibly empty");
         }
         ProducedType paramType = pr.getTypedParameter(p).getFullType();
@@ -2847,7 +2847,7 @@ public class ExpressionVisitor extends Visitor {
     
     @Override public void visit(Tree.Comprehension that) {
         super.visit(that);
-        that.setTypeModel(that.getForComprehensionClause().getTypeModel());
+        that.setTypeModel(that.getInitialComprehensionClause().getTypeModel());
     }
 
     @Override public void visit(Tree.SpreadArgument that) {
@@ -4629,13 +4629,13 @@ public class ExpressionVisitor extends Visitor {
                 }
                 else if (a instanceof Tree.Comprehension) {
                     ut = et;
-                    Tree.ForComprehensionClause fcc = ((Tree.Comprehension) a).getForComprehensionClause();
-                    result = fcc.getPossiblyEmpty() ? 
+                    Tree.InitialComprehensionClause icc = ((Tree.Comprehension) a).getInitialComprehensionClause();
+                    result = icc.getPossiblyEmpty() ? 
                             unit.getSequentialType(et) : 
                             unit.getSequenceType(et);
                     if (!requireSequential) {
                         ProducedType it = producedType(unit.getIterableDeclaration(), 
-                                et, fcc.getFirstTypeModel());
+                                et, icc.getFirstTypeModel());
                         result = intersectionType(result, it, unit);
                     }
                 }