using diff() in a program

[hpfx]

Thank you,
But I still have an issue,
in fact the expression comes from an input.
in that case, I saw that I must use a very strange INPUT syntax {{var,[2]}} in someone else post.

but when I do that :

Code:


EXPORT ABCD()
 BEGIN
 LOCAL a;
 INPUT({{a,[2]}});
 PRINT(diff(a,X));
 END;

I got Error: Bad Argument Type

my a var is supposed to be a string, like F9 in DrD code ?

I don't get the logic here...



Also INPUT builtin help is incomplete and wrong.

syntax : INPUT(var,...) *1st form syntax
and
var -> { var_name, [allowed_type_matrix] ... } *2nd form of var definition.

according this, I should be able to type INPUT({var_name},[types]})
but it gives an error ! I must type INPUT({{var_name, [types]}})

also, help is not complete, where is the list of types ? how can we guess ?