This is guards notation defined in user space.
If statements in Elm can get... verbose.
foo : Int -> String
foo x =
if x < 10 then
"x was small"
else if x > 100 then
"x was big"
else if x == 25 then
"x was 25 exactly"
else
"we hit default case"Guards help with all that
foo : Int -> String
foo x = x < 10 => "x was small"
|= x > 100 => "x was big"
|= x == 25 => "x was 25 exactly"
|= "we hit default case"Guards are usually compiler feature, its even one Elm had, but it was removed. There are 3 advantages to doing this in user space.
- Functions are total, (there is no way to avoid providing a default)
- Same tight notation as when supported by the compiler
- Fewer language features (user space is its own reward)
Guards make code more readable for simple flat expressions with lot of branches, not for times like this:
foo m a = case m of
Just x -> x >= 0 => "positive!"
|= x < 0 => (a == 100 => "wowzers!"
|= a > 100 => "trousers!"
|= "a wasn't cool")
|= case a of
0 -> "a was 0"
_ -> "who knows"
Nothing -> "murf"The above code will compile, but you should be sad if your code looks like that.
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