Version 2 (modified by chak, 10 years ago) (diff)


Closure conversion without a conversion class

The following scheme - if Roman doesn't find any problems with it (he is notorious for that) - should be simpler than what we had in mind so far for mixing converted and unconverted code.

Type declarations

If a type declaration for constructor T occurs in a converted module, we (1) generate a converted type declaration T_CC together two conversion functions fr_T and to_T, and (2) store these three names in the representation of T. Concerning Point (2), more precisely the alternatives of TyCon.TyCon get a new field tyConCC :: Maybe (TyCon, Id, Id). This field is Nothing for data constructors for which we have no conversion and Just (T_CC, fr_T, to_T) if we have a conversion.

Incidentally, if during conversion we come across a type declaration that we don't know how to convert (as it uses fancy extensions), we just don't generate a conversion.

Class declarations

If we come across a class declaration for a class C during conversion, we convert it generating C_CC. Like with type constructors, Class.Class gets a classCC :: Maybe Class field that is Just C_CC for classes that have a conversion. We also ensure that the classTyCon of C, let's call it T_C, refers to T_C_CC and fr_T_C and to_T_C in its tyConCC field, and that the classTyCon of C_CC is T_C_CC.

Instance declarations

If we encounter an instance declaration for C tau during conversion, there are two alternatives: we have a conversion for C or not:

  • if we do not have a conversion, we generate an instance (and hence dfun) for C tau^, where tau^ is the closure converted tau;
  • if we have a conversion, we generate an instance for C_CC tau^.

In any case, we add a field is_CC :: Just Instance to InstEnv.Instance that contains the additionally generated instance. And in both cases, we should be able to derive the required code for the dfun from the definition of C tau.

Type terms

We determine the converted type t^ of t as follows:

T^            = T_CC , if available
                T    , otherwise
a^            = a
(t1 t2)^      = t1^ t2^
(t1 -> t2)^   = Clo t1 t2
(forall a.t)^ = forall a.t^
(C t1 => t2)^ = C_CC t1^ => t2^ , if available
                C t1^ => t2^    , otherwise

Value bindings

When converting a toplevel binding for f :: t, we generate f_CC :: t^. The alternatives GlobalId and LocalId of Var.Var get a new field idCC :: Maybe Id and the Id for f contains Just f_CC in that field.