Release plans

[Simon Peyton-Jones]

| > - left-to-right impredicative instantiation: runST $ foo
|
| This concerns me.  With each ad-hoc extension of the type system, I
| worry that soon the GHC type system will become so byzantine and
| ill-specified that the type checker can only be cloned, not
| substantially improved on

On this one I am inclined to agree with you and Lennart.  I am dissatisfied with the story for impredicative instantiation, and I regard GHC's implementation as having a poor power-to-weight ratio.  I have not got as far as simply taking it out, yet, but sooner or later it has to change.  Dimitrios is working on variants which may help.

This is, incidentally, in contrast with most other of GHC's (admittedly complicated) extensions, most of which have a much better power-to-weight ratio.  (The other one I'm not happy about is the design for lexically scoped type variables.)

Simon

(PS: why the left-to-right thing?  The runST $ foo thing had become the number-one complaint, so I gave in!)