Note that there's some more recent research that bridges the HM-subtyping gap: http://stedolan.net/research/mlsub.pdf http://stedolan.net/research/mlsub.pdf S

Note that there's some more recent research that bridges the HM-subtyping gap: http://stedolan.net/research/mlsub.pdf http://stedolan.net/research/mlsub.pdf So this can be done, though afaik there's still some theory work to be done to combine it with some of the more advanced features in modern FP languages (e.g. higher rank types)