Struct definition

When writing programs we often need to access data that is more articulate than simple integers or booleans. For this reason plu-ts allows you to define custom data-types.

pstruct

To define your own type all you need is the pstruct typescript function.

pstruct takes as an argument an object that describes the structure of the new data-type and returns a Typescript class that represents our new type. You can also add custom methods to this structure, to make it more versatile.

The type of a struct definition (which is the argument of pstruct) is something like:

type StructDefiniton = {
    [constructor: string]: {
        [field: string]: TermType
    }
};

From this type we can already see that a struct can have multiple constructors (at least one) and each constructor can have 0 or more named fields.

This characteristic of having multiple constructors will allow for the creation of custom control flows through the use of pmatch described in its own section.

For now let's focus on defining some new structs and say we wanted to define a datatype that describes a Dog.

We could do so by writing:

// structs with single constructors acts in a similar way of plain typescript object
const Dog = pstruct({
    // single constructor
    Dog: {
        name: str,
        age: Age.type
    }
});

But our dog needs some toys to play with when we are out. So we define a structure that describes some toys:

const Toy = pstruct({
    Stick: {},
    Ball: {
        size: int,
        isSoft: bool
    },
    Mailman: {
        name: str,
        age: Age.type
    }
})

So now we can add a new field to better describe our dog:

const Dog = pstruct({
    Dog: {
        name: str,
        age: Age.type,
        favouriteToy: Toy.type
    }
});

IMPORTANT

When defining a struct the order of the constructors and the order of the fields matters.

In fact at UPLC level there are no names.

This does have two important implications:

1. structs with similar definition will be interchangeable; meaning that something like the snippet below can be used in place of a Dog without anything breaking

const Kid = pstruct({
    Kid: {
        name: str,
        age: Age.type,
        toy: Toy.type
    }
});

2. changing the order of constructors or fields gives back a totally different struct

struct values

To build a plu-ts value that represents a struct you just use one of the constructors you defined.

So if you where to create an instance of a Dog you'd just write:

const myDog = Dog.Dog({

    name: pStr("Pluto"),
    age:  Age.from( pInt(3) ),

    favouriteToy: Toy.Mailman({
        name: pStr("Bob"),
        age:  Age.from( pInt(42) )
    })

})

struct plu-ts type

Like aliases, structs also do have custom plu-ts types; which can be accessed using the type static property

const typeOfToy = Toy.type;