Add type checking for default values and emit them in C++

trans/transpiler/phases/emit_cpp/block.py

@@ -61,14 +61,18 @@ class BlockVisitor(NodeVisitor):
             yield f"{node.name}_inner::"
         yield "operator()"
         yield "("
-        args_iter = zip(node.args.args, node.type.parameters)
+        padded_defaults = [None] * node.type.optional_at + node.args.defaults
+        args_iter = zip(node.args.args, node.type.parameters, padded_defaults)
         if skip_first_arg:
             next(args_iter)
-        for i, (arg, argty) in enumerate(args_iter):
+        for i, (arg, argty, default) in enumerate(args_iter):
             if i != 0:
                 yield ", "
             yield from self.visit(argty)
             yield arg.arg
+            if emission == FunctionEmissionKind.DECLARATION and default:
+                yield " = "
+                yield from self.expr().visit(default)
         yield ")"
 
         inner_scope = node.inner_scope

trans/transpiler/phases/typing/block.py

@@ -156,7 +156,9 @@ class ScoperBlockVisitor(ScoperVisitor):
         scope.function = scope
         node.inner_scope = scope
         node.type = ftype
-        ftype.optional_at = 1 + len(node.args.args) - len(node.args.defaults)
+        ftype.optional_at = len(node.args.args) - len(node.args.defaults)
+        for ty, default in zip(argtypes[ftype.optional_at:], node.args.defaults):
+            self.expr().visit(default).unify(ty)
         for arg, ty in zip(node.args.args, argtypes):
             scope.vars[arg.arg] = VarDecl(VarKind.LOCAL, ty)
         self.fdecls.append((node, rtype.return_type))