All free variables in a GAP function have a static binding within its lexicographical closure. In the original program the same i is a free variable in each function and the lexicographical closure is global name space. Hence any modification of i changes all the function definitions.
factory := function(i) local f; f := function(n) return n+i; end; i:=5; return f; end; The lexicographical closure of the variable i is the factory function definition. Since i is free in f and the last assignment is within the lexicographical closure of i we have changed the function definition. f1 := factory(1); f2:=factory(2); f1(1) ---> returns 6 f2(1) ---> returns 6 In the example I gave before and F := List([1..5], i -> (n -> n + i)); we lose access to the lexicographic scope of i and the values are fixed as desired. Robert F. Morse On Wed, Sep 11, 2013 at 3:10 PM, Bill Allombert <bill.allomb...@math.u-bordeaux1.fr> wrote: > On Wed, Sep 11, 2013 at 11:34:58AM -0500, Robert Morse wrote: >> The value of the variable i is not bound at function definition. >> Rather, whatever i 's value at function execution is what is used. > > Please excuse my curiosity as someone who wrote some computer algebra system > interpretor. > Are you saying that i is a global variable which is dynamicaly scoped ? > >> After the loop the variable i has the value 5. Hence calling each >> instance F[i] returns the same value. >> >> You can accomplish what you want by writing a function that creates >> the function (binding the value i): >> >> factory := function(i) return function(n) return n+i; end; end; > > and there i is function parameter which is lexicaly scoped, > and functions are closed over lexicaly scoped variable ? > > Cheers, > Bill. > > _______________________________________________ > Forum mailing list > Forum@mail.gap-system.org > http://mail.gap-system.org/mailman/listinfo/forum _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
