Implement and test resultchild, which allows something other than the final statement of a QAST::Stmt or QAST::Stmts to be used as the result of the overall operation.

Author: jnthn

src/QAST/Compiler.nqp

@@ -365,25 +365,30 @@ class QAST::Compiler is HLL::Compiler {
     }
 
     multi method as_post(QAST::Stmts $node) {
-        self.compile_all_the_stmts($node.list)
+        self.compile_all_the_stmts($node.list, $node.resultchild)
     }
 
     multi method as_post(QAST::Stmt $node) {
         my $orig_reg := $*REGALLOC;
         {
             my $*REGALLOC := RegAlloc.new($orig_reg);
-            self.compile_all_the_stmts($node.list)
+            self.compile_all_the_stmts($node.list, $node.resultchild)
         }
     }
 
-    method compile_all_the_stmts(@stmts) {
+    method compile_all_the_stmts(@stmts, $resultchild?) {
         my $last;
         my $ops := self.post_new('Ops');
+        my $i := 0;
         for @stmts {
             $last := self.as_post($_);
             $ops.push($last);
+            if nqp::defined($resultchild) && $resultchild == $i {
+                $ops.result($last.result);
+            }
+            $i := $i + 1;
         }
-        if $last {
+        if $last && !nqp::defined($resultchild) {
             $ops.result($last.result);
         }
         $ops

src/QAST/Stmt.nqp

@@ -1,2 +1,5 @@
 class QAST::Stmt is QAST::Node {
+    has $!resultchild;
+
+    method resultchild(*@value) { $!resultchild := @value[0] if @value; $!resultchild }
 }

src/QAST/Stmts.nqp

@@ -1,2 +1,5 @@
 class QAST::Stmts is QAST::Node {
+    has $!resultchild;
+
+    method resultchild(*@value) { $!resultchild := @value[0] if @value; $!resultchild }
 }

t/qast/qast.t

@@ -1,6 +1,6 @@
 use QAST;
 
-plan(68);
+plan(70);
 
 # Following a test infrastructure.
 sub compile_qast($qast) {
@@ -970,3 +970,26 @@ is_qast(
     ),
     115,
     'QAST::VM with pirop and signature after a space');
+
+is_qast(
+    QAST::Block.new(
+        QAST::Stmts.new(
+            :resultchild(0),
+            QAST::IVal.new( :value(1) ),
+            QAST::IVal.new( :value(2) )
+        )
+    ),
+    1,
+    'resultchild works on QAST::Stmts');
+
+is_qast(
+    QAST::Block.new(
+        QAST::Stmt.new(
+            :resultchild(1),
+            QAST::IVal.new( :value(3) ),
+            QAST::IVal.new( :value(4) ),
+            QAST::IVal.new( :value(5) )
+        )
+    ),
+    4,
+    'resultchild works on QAST::Stmt');