Records

A record is a composite of other types of data, each of which is named. OCaml records are much like structs in C.

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type ptype = TNormal | TFire | TWater
type mon = {name : string; hp : int; ptype : ptype}

To build a value of a record type, we write a record expression, which looks like this:

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{name = "Charmander"; hp = 39; ptype = TFire}

To access a record and get a field from it, we use the dot notation that you would expect from many other languages. For example:

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let c = {name = "Charmander"; hp = 39; ptype = TFire};;
c.hp

It’s also possible to use pattern matching to access record fields:

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match c with {name = n; hp = h; ptype = t} -> h

The n, h, and t here are pattern variables. There is a syntactic sugar provided if you want to use the same name for both the field and a pattern variable:

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match c with {name; hp; ptype} -> hp

Tuples

Like records, tuples are a composite of other types of data. But instead of naming the components, they are identified by position. Here are some examples of tuples:

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(1, 2, 10)
(true, "Hello")
([1; 2; 3], (0.5, 'X'))

A tuple with two components is called a pair. A tuple with three components is called a triple. Beyond that, we usually just use the word tuple instead of continuing a naming scheme based on numbers.