CODEWITHSUNDEEP
syntaxpattern-matchingocaml
cdsjqhfjidql
cdsjqhfjidql

Reputation: 19

Why || can't be used in pattern matching?

In OCaml when I do a pattern matching I can't do the following:

let rec example = function
   | ... -> ...
   | ... || ... -> ... (* here I get a syntax error because I use ||*)

Instead I need to do:

let rec example1 = function
     |... -> ...
     |... | ... -> ...

I know that || means or in OCaml, but why do we need to use only one 'pipe' : | to specify 'or' in pattern matching?

Why don't the usual || work?

Upvotes: -1

Views: 93

Answers (1)

glennsl
glennsl

Reputation: 29106

|| doesn't really mean "or" generally, it means "boolean or", or rather it's the boolean or operator. Operators operate on values resulting from the evaluation of expressions, its operands. Operations and operands together also form expressions which can then be used as operands with other operators to form further expressions and so on.

Pattern matching on the other hand evaluate patterns, which are neither boolean or expressions. Although patterns do in a sense evaluate to true or false if applied to, or rather matched against, a value, they do not evaluate to anything on their own. They are in that sense more like operators than operands. Furthermore, the result of matching against a pattern is not just a boolean value, but also a set of bindings.

Using || instead of | with patterns would overload its meaning and serve more to confuse than to clarify I think.

Upvotes: 2

Related Questions