Elm:
Concatenating strings

How to:

Elm’s got a neat operator (++) to save the day:

greeting : String
greeting =
    "Hello, " ++ "world!"

-- "Hello, world!"

But sometimes, you’ve got a bunch of pieces. Fear not, ++ is chainable:

fullName : String
fullName =
    "Elm" ++ " " ++ "Lang"

-- "Elm Lang"

And for lists of strings, String.join is your friend:

words : List String
words =
    ["Join", "the", "Elm", "club"]

sentence : String
sentence =
    String.join " " words

-- "Join the Elm club"

Deep Dive

Back in the day, you’d often concatenate strings with complex functions in other languages. In Elm, it’s always been a breeze thanks to the (++) operator. If you’re really concatenating a lot, efficiency could come into play; using (++) on long strings may be slower, because Elm has to walk through the entire string on the left of (++) every time.

There’s also “interpolation” in some languages, but Elm doesn’t do string interpolation. No worries though, (++) and String.join have us covered.

Under the hood, when Elm concatenates, it tries to be smart about it, often using optimized JavaScript operations, which is what Elm compiles down to in the end. So even if (++) can seem simple, there’s some cleverness going on behind the scenes to keep things zippy.

See Also

• Elm official documentation on Strings: https://package.elm-lang.org/packages/elm/core/latest/String
• Elm Guide, where you can learn more about strings: https://guide.elm-lang.org/strings/