On Nov 13, 2007 10:56 AM, John Lato
I know there are several important differences between let-expressions and where-clauses regarding scoping and the restriction of "where" to a top-level definition. However, frequently I write code in which
One place I find it useful is when there is a common computed value that is used throughout a function definition. For example, imagine some function that uses the length of a list passed in: someFunction ls a b c = ... (length ls) where someAuxFunction x y = ... length ls .. someOtherFunction x y = ... length ls ... a where clause can capture that calculation, make sure it's only done once, and shared throughout the function definition: someFunction ls a b c = ... listLen ... where listLen = length ls someAuxFunction x y = ... listLen ... someOtherFunction x y = ... listLen ... Notice a let clause wouldn't do it above, because "length ls" is called inside other functions defined in the where clause. Of course everything could be moved to a "let" clause in the function body. At that point I think it's purely stylistic. Justin