Can this expression be written without brackets or back-ticks?

Question

mul (add 2 3) 5

Can the dot (.) and dollar ($) operators alone replace the brackets? The mul and add functions are filler, i.e. the order of application must stay the same. This is an exercise to better understand the aforementioned operators.

Fully replace the brackets, or is it allowed to introduce new ones? — Willem Van Onsem, Feb 04 '17 at 18:21
Use of the where clause works and scales up well to more complex examples. `mul s 5 where s = add 2 3` — Ware, Feb 04 '17 at 18:30

score 1 · Answer 1 · edited Feb 05 '17 at 04:04

1

You can use the combinator flip to allow you to reverse the order of the arguments. each following line is equivalent:

mul (add 2 3) 5
(flip mul) 5 (add 2 3)
flip mul 5 $ add 2 3

flip is defined as simply:

flip :: (a -> b -> c) -> (b -> a -> c)
flip f b a = f a b

However, I don't believe the two operators . and $ alone are sufficient

edited Feb 05 '17 at 04:04

duplode

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answered Feb 05 '17 at 03:19

Zoey Hewll

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I think that is as close as we can get if the requirements of the OP are taken literally. – duplode Feb 05 '17 at 04:05

score 0 · Answer 2 · answered Feb 04 '17 at 18:53

0

You could use the algebraic properties of mul:

mul 5 $ add 2 3

answered Feb 04 '17 at 18:53

Thomas M. DuBuisson

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If and only if the actual used function has that property, see "the mul and add functions are filler". – Zeta Feb 04 '17 at 19:14
Certainly, that line was intended to be interpreted as a precondition. – Thomas M. DuBuisson Feb 04 '17 at 20:48

Can this expression be written without brackets or back-ticks?

2 Answers2