On Tue, Jun 17, 2014 at 03:25:10AM -0700, Alexey Muranov wrote:
Is this the expected behavior that
1 = 0
does not raise any error? What does this mean?
The general syntax of assignments is pattern = expression One most often uses a pattern consisting of a single variable, but any pattern will do. (For example, try writing [x,y,z] = [1,2,3] as a top-level declaration and see what happens!) 1 is a pattern which matches the number 1. 0 is obviously an expression. Of course, the pattern 1 does not match the expression 0. However, binding is lazy: for example, writing [x,y] = [1,2,3] does not in and of itself cause an error; it will only cause an error if you try to use x or y. However, since the pattern 1 contains no variables, there is no way to ever force the pattern-matching to actually take place. So 1 = 0 just sits there, sort of like an ugly, angry dog who wants to bite people except that it is locked in a cage with no door. Occasionally people walking by look at it pityingly, but mostly no one pays it any attention. -Brent