[Haskell-cafe] Request for help w/ Ex. 10 in *Arrows and Computation*.

David Banas capn.freako at gmail.com
Sat Oct 22 13:42:14 UTC 2016

Hi all,

I’m stuck in Ex. 10 of *Arrows and Computation*, by Ross Paterson:
https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/blob/master/Arrows_and_Computation/Arrows_and_Computation.html#ex9 <https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/blob/master/Arrows_and_Computation/Arrows_and_Computation.html#ex9>

It seems to me that if, in the third step of my proof, I could convert the *left (pure fst)* into *left (first <?>)*, then I could use the **distribution** axiom to convert *pure distr >>> left (first <?>)* into *first (left <?>) >>> pure distr *. At that point, I would have (starting from the left side of my expression): *first (..) >>> first (..)*, and could apply the functor property of *first*, in order to simplify the expression.


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