CODEWITHSUNDEEP
pattern-matchingocamlrecord
choeger
choeger

Reputation: 3567

What is the meaning of the open record pattern?

OCaml has an explicit syntactic construct (See Parsetree.pattern_desc, constructor Ppat_record) to discriminate between "open" and "closed" record patterns.

This seems to have no influence whatsoever on the pattern matching:

utop # type r = {repr:int; foo:int} ;;
type r = { repr : int; foo : int; } 
utop # let f = function {repr} -> repr;;
val f : r -> int =  <fun> 
utop # let g = function {repr;_} -> repr;;
val g : r -> int = <fun>

So what is/was its purpose? Is this some kind of SML relic?

Upvotes: 1

Views: 146

Answers (1)

Thomash
Thomash

Reputation: 6379

It is just a language extension to tell the compiler that you ignored some fields on purpose so that you can have a warning when you forget a field.

http://caml.inria.fr/pub/docs/manual-ocaml/extn.html#sec226

Upvotes: 2

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