tsani / fuckdown2 Goto Github PK

Using MonadFix on free monads doesn't work 😢

One strategy could be to use a string-based lookup table for label offsets that is built by first assuming that all labels have offset zero, and then passing back over the structure to fill in the zeroes with the real offsets.

Another strategy could be to implement some kind of forward declaration of labels as a monadic action, e.g.

do
lab <- newLabel -- the label offset is undecided
cmp rax 0
je lab
-- interesting code
label lab -- the current code offset is set as the label offset

This strategy has the benefit of making the labels "anonymous", as in the current formulation. Furthermore, it can be made to be backwards compatible with the backwards-only labelling system that's already in place. (Specifically, the label function that currently exists can be implemented as newLabel >>= label in the new model; it suffices to avoid a name collision now between the old label function and the new one.)