Implement returning from functions.

src/Snake/Actions.nqp

@@ -118,6 +118,13 @@ method simple-statement($/) {
 
 method ordinary-statement:sym<EXPR>($/) { make $<EXPR>.ast; }
 method ordinary-statement:sym<pass>($/) { make QAST::Stmts.new(); }
+
+method ordinary-statement:sym<return>($/) {
+    # TODO: Bare return should return None.
+    make QAST::Op.new(:op<call>, :name<$RETURN>,
+        $<EXPR> ?? $<EXPR>.ast !! QAST::Stmts.new());
+}
+
 method ordinary-statement:sym<break>($/) { make QAST::Op.new(:op<control>, :name<last>); }
 method ordinary-statement:sym<continue>($/) { make QAST::Op.new(:op<control>, :name<next>); }
 
@@ -160,12 +167,19 @@ method compound-statement:sym<for>($/) {
         ))
 }
 
+# TODO: A function without an explicit return should return None in Python. We
+# currently have the same semantics as Perl (and others), returning the value
+# of the last statement in the block.
 method compound-statement:sym<def>($/) {
     # TODO: Check for $*IN_CLASS and push_s name to @*METHODS if true.
     my $block := $<new_scope>.ast;
     my $name := $<identifier>.ast.name;
     $block.name: $name;
 
+    if $*HAS_RETURN {
+        $block[1] := QAST::Op.new(:op<lexotic>, :name<$RETURN>, $block[1]);
+    }
+
     my $ast := QAST::Stmts.new(QAST::Op.new(:op<bind>,
             QAST::Var.new(:name($name), :scope<lexical>),
             $block));

src/Snake/Grammar.nqp

@@ -44,6 +44,7 @@ method TOP() {
     my $*DEFAULTS := 0;
 
     my $*IN_CLASS := 0;
+    my $*IN_DEF := 0;
 
     return self.file-input;
 }
@@ -243,6 +244,11 @@ token simple-statement { <stmt=.assignment> || <stmt=.ordinary-statement> }
 proto token ordinary-statement {*}
 token ordinary-statement:sym<EXPR> { <EXPR> }
 token ordinary-statement:sym<pass> { <sym> }
+# TODO: Return actually takes a list of expressions, not a single one.
+token ordinary-statement:sym<return> {
+    <sym> <.ws> <EXPR>?
+    [ <?{ $*IN_DEF == 1 }> {$*HAS_RETURN := 1} || <.panic: "Can only return when inside a function."> ]
+}
 
 # TODO: Handle all possible assignments.
 rule assignment { <identifier> '=' <EXPR> }
@@ -282,6 +288,8 @@ token compound-statement:sym<def> {
     [:s<sym> <identifier>
     {Snake::Actions.add-declaration: $<identifier>.ast.name}
     '(' ~ ')' <parameter_list> ':'
+    :my $*IN_DEF := 1;
+    :my $*HAS_RETURN := 0;
     <new_scope>]
 }
 
@@ -292,6 +300,7 @@ token compound-statement:sym<class> {
     {Snake::Actions.add-declaration: $<identifier>.ast.name}
     ':'
     :my $*IN_CLASS := 1;
+    :my $*IN_DEF := 0;
     :my @*METHODS := nqp::list_s();
     <new_scope>]
 }