Emit default values for lambda parameters

trans/transpiler/phases/emit_cpp/block.py

@@ -78,7 +78,7 @@ class BlockVisitor(NodeVisitor):
             else:
                 yield from self.visit(argty)
             yield arg.arg
-            if emission == FunctionEmissionKind.DECLARATION and default:
+            if emission in {FunctionEmissionKind.DECLARATION, FunctionEmissionKind.LAMBDA} and default:
                 yield " = "
                 yield from self.expr().visit(default)
         yield ")"