Ino

Ino is a DSL to generate data structures for golang.

Install

go install github.com/nihei9/ino/cmd/ino@latest

Usage

First, save your source code written in Ino to a file with the extension .ino. In this example, let's say you saved the file named example.ino.

Next, convert the source code in Ino to golang using ino command. --package flag allows you to change the package name. The default package name is main.

ino --package example

Then you will get a file named example.go.

You can also use go:generate directive.

//go:generate ino --package example

Ino syntax and available Go APIs

data

data keyword allows you to generate a sum type.

Example: Basic usage

In Ino

data Pen
    = BallpointPen string
    | FountainPen
    ;

Go APIs generated

The following three public APIs are available.

• Pen interface
• BallpointPen function (constructor) that returns a Pen object
• FountainPen function (constructor) that returns a Pen object

Now, you can check that a value of Pen is which variant using OK method and can retrieve fields using Fields method.

bB := BallpointPen("Black")
ok := bB.Maybe().BallpointPen().OK()            // true
ok = bB.Maybe().FountainPen().OK()              // false
color, ok := bB.Maybe().BallpointPen().Fields() // "Black", true
color, ok = bB.Maybe().FountainPen().Fields()   // "", false

f := FountainPen()
ok = f.Maybe().FountainPen().OK()  // true
ok = f.Maybe().BallpointPen().OK() // false

👀 Fields method isn't available in FountainPen because it has no fields.

Example: Generics #1

You can define polymorphic types using type variables.

In Ino

Type variables can follow a data type name. In this example, a is a type variable.

data Option a
    = None
    | Some a
    ;

Go APIs generatd

• Option[T1 any] interface
• None function that returns a Option object
• Some[T1 any] function that returns a Option object

s1 := Some(100)           // Option[int]
n := None[int]            // Option[int]
s2 := Some(Some("Hello")) // Option[Option[string]]

num, ok := s1.Maybe().Some().Fields()  // 100, true
opt, ok := s2.Maybe().Some().Fields()  // Some("Hello"), true
str, ok := opt.Maybe().Some().Fields() // "Hello", true

Example: Generics #2

Polymorphic-type literals must be enclosed in parentheses.

data List a
    = Nil
    | Cons a (List a)
    ;