[Aldor-l] Specifying properties of functions

[Ralf Hemmecke]

Hello,

In the algebra library we have something like this

define CommutativeRing: Category == Ring with {...}

It is implicitly understood that * is the function that "commmutative" 
refers to.

A more flexible way to state properties of functions in Aldor would be
something like this.

define Commutative(D: Type, f: (D, D) -> D): Category == with;
define MyCommutativeRing: Category == MyRing with Commutative(%, *$%);

Of course, there is still a language feature missing to express, 
"f(x,y)=f(y,x)", but at least, such a property would be explicitly 
stated through a category.

Unfortunately, the attached file does not compile. The compiler claim
that it cannot figure out what * is.

Does anybody know how I would have to rewrite the program so that the
compiler accepts it?

Best regards

Ralf
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