[Haskell-cafe] Why are && and || right-associative?
jerzy.karczmarczuk at unicaen.fr
Fri Apr 19 19:43:46 UTC 2019
Le 19/04/2019 à 19:31, Albert Y. C. Lai a écrit :
> I am late to this discussion but here is my solution.
> This is really just story-telling to end-users.
> The real story you want to tell everyone is this: "x && y && z && t"
> means Scheme's "(and x y z t)", and it means you try the sequence from
> left to right, stopping at the first incident of "false".
> As many of you have observed, it doesn't matter, a compiler writer
> already knows it's "(and x y z t)" and generates the correct code and
> not bother to split hair.
Very, ehm, interesting methodology...
I suspect that you missed that part of the discussion where people
discussed parsing. I don't know if you ever taught compilation, but
imagine that your students ask you:
*/HOW /**/"x && y && z && t" is transformed into /**/"(and x y z t)" ?/*
Will your answer be:
*/it doesn't matter, a compiler writer already knows it's "(and x y z
t)" and generates the correct code and not bother to split hair/*
Everybody will be happy. Bon courage.
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