I'm currently reading a C++ tutorial. (Don't ask!) Of course, C++ is that crazy language where *assignment* is actually an *operator*. Sick, sick people... The tutorial pointed out that "x = 4" is a legal assignment, but "4 = x" is not. "Obviously that would be silly." Now it occurs to me... in Haskell, "4 = x" is actually a perfectly legal thing to say. (!) It's pretty pointless, but it's legal. For example: foo x = let 4 = x in 2*x which, as best as I can tell, does exactly the same thing as (2*). In a similar vein, one might write foo x = do let 4 = x return (2*x) which also does more or less the same as (return). However, consider the following: foo :: Int -> Maybe Int foo x = do 4 <- return x return (2*x) This, it turns out, is an extremely odd way of checking whether x == 4. All of this works of course because in Haskell, "=" is not an assignment, it's a definition, and the RHS is not a variable, it's a pattern. And "4" is a perfectly legitimate pattern. Now, if only I could find a use for all this that borders on "useful"...! ;-)