[sfvisser]

If you really need to run your computations in a separate context/arrow, making them explicit in the types is nice. Having general syntactic rules to build, compose and run them: great.

However, if you can avoid the additional arrow entirely: even better!

I mean Haskell of all languages has green threads and doesn’t need the entire promise shenanigans.

Even in Haskell I sometimes I build very specific DSLs for my domain to be interpreted in a separate step so I can freely fix my pure and impure code.