Here we summarise aspects of Green Card that are less than ideal, and
indicate possible improvements.
Automatic DIS generation.
Pretty much every newtype or single-constructor declaration
that is involved in a foreign language call needs a corresponding
%dis definition. Maybe this %dis
definition should be automated. On the other hand, there are many
fewer data types than procedures, so perhaps it isn't too big a burden
to define a %dis for each.
Alternatively, go the other way and have Green Card generate a Haskell type
from a %dis definition, along the lines of what %enum
The error handling provided by %fail is fairly rudimentary.
It isn't obvious how to improve it in a systematic manner though.