Lifting a pipe to work on tuples

Question

141 views Asked by utdemir At 26 December 2016 at 10:05

I need a function with type Pipe a b m r -> Pipe (a, c) (b, c) m r.

But no matter how much I play with for, ~> or >~; I can not match the types properly.

Can you help me?

There are 1 answers

**Daniel Wagner** · Accepted Answer · 2016-12-26T10:24:10+00:00

Daniel Wagner On 26 December 2016 at 10:24 BEST ANSWER

I don't think it's possible in general. Suppose we did manage to write it:

hypotheticalLift :: Pipe a b m r -> Pipe (a, c) (b, c) m r

What behavior should hypotheticalLift (yield b) have? Presumably it should be the same as yield (b, c) for some c -- but which c, and why?