Joël Quenneville:

Our world is full of uncertainty. This uncertainty bleeds into our programs. A common way of dealing with this is null/nil. Unfortunately, this leads to even more uncertainty because this design means any value in our system could be null unless we’ve explicitly checked it’s presence.

Imagine how many developer-hours are wasted globally each year dealing with null/nil. The number would probably astound us.

The major advantage of guard clauses is to suss out invalid inputs (often nils) at the perimeter of your program/module/function, so the rest of your code doesn’t have to concern itself with these uncertainties. But Maybe there’s another way…

In Elm, all values are guaranteed to be present except for those wrapped in a Maybe. This is a critical distinction. You can now be confident in most of your code and the compiler will force you to make presence-checks in places where values are optional.

Click through to learn the mechanics of it all.