Operator precedence

On 5 September 1996, Nils M. Holm asks:


> Given a language without any operator precedence, would you prefer
>
> 1) evaluation from the left to the right, like a sequence of identical
> Operations in C [a - b + c = (a - b) + c]
>
> or
>
> 2) evaluation from the right to the left, like in APL?
> [a - b + c = a - (b + c)]
>
> What are the reasons for your choice?


There are 2 related reasons APL chooses right to left precedence:


        1) the language supports the notion of applying a function across
                an array, e.g. +/1 2 3 <-> 1 + 2 + 3, or (for infix function f)
                f / 1 2 3 <-> 1 f 2 f 3;


        2) for a non-commutative function, such as minus, the result is much
                more interesting evaluated right to left, e.g. -/1 2 3 4 5
                becomes the alternating sum (((1 - 2) + 3) - 4) + 5; if evaluation
                were as in conventional mathematics, this would be equivalent
                to the less interesting 1 - (2 + 3 + 4 + 5).


                Similarly, division across a vector gives a continued fraction
                instead of the first number divided by the product of the remaining
                numbers.


I can find the citation of this if you are interested.
--
Devon McCormick
devon_mccormick@smb.com
--

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