[Aldor-l] Specifying properties of functions

[Martin Rubey]

Dear Ralf,

one way to get it to compile is to say 

define MyCommutativeRing: Category == with {MyRing; *: (%, %) -> Integer; 
                                            Commutative(%, *$%)};

however, I was unable to determine whether that would "work".

Martin

Ralf Hemmecke writes:
 > 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