Maple wrong about partial derivative of exponential function?

Question

When I input this function in Maple:

f := (x, y) -> exp(x+xy-2*y)

And take the derivative:

diff(f(x, y), x);

I receive:

exp(x + xy - 2 y)

But I would have expected it to be:

(1+y)exp(x+xy-2y)

Does anyone have an explanation for this?

Answer 1

Maple understand each (non-predefined) expression of the form abcde as one variable. It also works for Mathematica where abcde means one variable while a b c d e is understood as a product of $5$ variables. Spaces does not work for Maple formulas typed in plain text, so you have to use * each time you want to multiply (works as well for Mathematica).