Re: User definable operators

>>example, "f(a+b)" means either f evaluated at a + b, or f times a + b,
>>depending whether f is a function or not. If you consider that
>>functions can really be expressions too (like (f \compose g)(a + b))
>>things get worse. Mathematica uses [] for functions for this very
>>reason.
>
>This particular ambiguity is typically blocked in most computer
>languages anyhow. In any of them, using xy for the product of x and y
>is prohibited, and I know of none for which even 2x is allowed.


I know of a couple that allow this sort of thing.
HAL and HAL/S (basically an extension of PL/1) allow things like


X = A X + Y


meaning X is replaced by the sum of Y and the product of A and X. Of
course, they also allowed things like superscripts and subscripts, and
had matrices and vectors along with primitives to operate upon them.


A more interesting example, perhaps, is Metafont, Knuth's language for
specifying type fonts.


Preston Briggs
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