Re: [q-lang-users] Strong examples of Q equational programming wanted

[Greg B. <gr...@sl...>]

Albert Graef wrote:
> Thanks a lot, Greg, for the very illustrative examples. You might wish
> to compare those with the Q script at
> http://q-lang.sf.net/examples/symbolic.q
> 
> This illustrates my point very well -- even though those rules are in
> fact fairly trivial, you really have to go to some lengths to implement
> them in a more conventional language. Q makes this kind of stuff very
> easy precisely because expressions are first-class and "definitions" are
> just rewriting rules, so that you can just write down the rules "as is".

    As long as we're getting off-topic, here's another Haskell exmaple
using algebraic data types...

    http://sleepingsquirrel.org/lisp/diff_ADT.html

...and a Prolog solution...


diff(X,X,1).
diff(U+V,X,Z) :- diff(U,X,Up), diff(V,X,Vp), simp(Up+Vp,Z),!.
diff(U*V,X,C) :- diff(U,X,Up), diff(V,X,Vp),
                 simp(U*Vp,A), simp(V*Up,B), simp(A+B,C),!.
diff(_,X,0).

simp(0*X,0).
simp(X*0,0).
simp(1*X,X).
simp(X*1,X).
simp(0+X,X).
simp(X+0,X).
simp(X,X).