Pattern and expression language asymmetry

Learning
1

I’m always surprised by the following asymmetry between the pattern and expression language:

# type t = A of string;;
type t = A of string
# function Some A "bla" -> true | _ -> false;;
- : t option -> bool = <fun>
# let v = Some A "bla";;
Error: Syntax error
# let v = Some (A "bla");;
val v : t option = Some (A "bla")

Somehow I don’t see where the parenthesis constraint occurs in the expression language.

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2

It appears in the precedence table, where it is stated that constructor application is left associative, hence the need for parentheses when you need to associate to the right.

I did not know that this was not case the case for patterns. I suppose the difference is that, in patterns, you cannot have function applications, so constructor applications can be made right-associative.

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