1–10 of 28 posts
y = x + ++x
What is y?
Even the professor who teaches compiler construction at my university thought it was interesting to see how different languages or compilers handle this. I've tried a couple but leave it to you to post and discuss your results.
(I know it's terrible code)
(let* ((x 10)
(y x))
(+ x (incf x)))
vs
(let* ((x 10)
(y x))
(prog1
(+ x x)
(incf x)))
[INCF does it with side-effects, use 1+ or directly evaluate (+ 1 x) for the clean version]
:)
(let* ((x 10) (y x)) (+ x (incf x))) vs (let* ((x 10) (y x)) (prog1 (+ x x) (incf x))) [INCF does it with side-effects, use 1+ or directly evaluate (+ 1 x) for the clean version] Not everyone puts up with semantic ambiguity in operator precedence and evaluation. Some of us program in parse trees, directly :-)
My_Favourite_Compiler would compile "x + ++x" as a call to abort(3). I think "undefined behaviour" is a horrible idea.
>>> x = 10
>>> x + ++x
20
expression( ... ++x ... )
x = x+1;
expression( ... x ... )
1. put x=x+1 before the expression
2. replace ++x with x
But in languages where + is a function there's a good chance you get 21.
Interpreter, really: >>> x = 10 >>> x + ++x 20 I suspect my other favorite compiler will say 'Type error: Could not match "Num a => a" against "Num a => [a] -> [a]"', but I don't want to wait for it to finish installing.