Cookbooks
Elm
Chapter 5. Good Coding Practices
Handling errors

Elm:
Handling errors

How to:

Elm’s core philosophy is No Runtime Exceptions. So, Elm leverages its type system with types like Maybe and Result to handle errors.

For Maybe scenario:

safeDivide : Float -> Float -> Maybe Float
safeDivide numerator denominator =
    if denominator == 0 then
        Nothing
    else
        Just (numerator / denominator)
        
-- When you run it:

safeDivide 10 2
--> Just 5

safeDivide 10 0
--> Nothing

For Result scenario:

type Error = DivisionByZero

safeDivide : Float -> Float -> Result Error Float
safeDivide numerator denominator =
    if denominator == 0 then
        Err DivisionByZero
    else
        Ok (numerator / denominator)

-- And using it:

safeDivide 10 2
--> Ok 5

safeDivide 10 0
--> Err DivisionByZero

Deep Dive

Elm’s type system is strict, which helps catch errors early. Historically, most languages relied on exceptions and runtime checks, but Elm chose compile-time guarantees. Alternatives like Result allow detailed error info, while Maybe is simpler for yes-no scenarios. Elm’s error handling encourages developers to consider all paths upfront, avoiding the pitfalls of forgotten error cases.

See Also:

Logging