Operator :: OCaml

Question

I am a beginner in OCaml and trying to build a parser, I want to have a list that stores all the methods in my class. This is one part that I have in my .mly file.

init_method_list: 
    { [] }
    | method_list method_decl { List.rev($1) }
;

method_list:
    method_decl { [ $1 ] }
    | method_list method_decl { $2 :: $1 }
;

Can anyone explain exactly what's going on here? Especially the :: operation. Been googling around but couldn't find the operator in the docs.

I get that the list can be empty, or we make right recursive calls to fill it up with all the methods in class. method_decl just looks for the match of the specific token combinations that represents a method.

In Ocaml, the operator `::` is use to concatenate an element of type `'a` to a list of type `'a list`. — alifirat, Sep 11 '15 at 12:29
okay thanks, does it prepend the element to the front of the list? @alifirat — novalain, Sep 11 '15 at 13:33
What did you google for? I just googled "ocaml tutorial" and on the first hit there's the basic tutorial which uses "::" — , Sep 11 '15 at 19:56

score 4 · Accepted Answer · answered Sep 11 '15 at 13:45

4

As I said in my comment, the operator :: is use to concatenate an element of type 'a to a list of type 'a list. A little example :

1 :: [2;3] produces the list [1;2;3] so yes it prepend the element to the front of the list.

answered Sep 11 '15 at 13:45

alifirat

2,899
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The `::` is not really an operator but rather a syntactic notation – this why it is allowed to appear in matching patterns while operators are not. – Michaël Le Barbier Apr 28 '16 at 12:44

score 0 · Answer 2 · answered Jun 07 '16 at 12:11

0

As everyone else said, :: concatenates an element onto a list of the same type. As just an extra aside, if you need to concatenate two lists, you can use the @ symbol, for example:

[1;2;3]@[4] will give the list [1;2;3;4]

answered Jun 07 '16 at 12:11

issharp

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Operator :: OCaml

2 Answers2