goto

Goto is a programming language that can be mixed with Go.

Design Principles

Ecosystem Compatibility over Perfection
- Given multiple similarly good solutions, we aim to choose the best that maintains compatibility with packages written in Go. While we prefer using sum-type enums for errors, providing syntactic sugar for the usual if err != nil pattern is a sufficient improvement that works better with how existing Go projects work.
Balance Familiarity and Readibility
- Even though we have a strong preference for Rust-like syntax, we apply syntactic changes only where we find Go's syntax to be overly cluttered or hard to read. That means we use func Function(a uint8) string instead of pub fn Function(a: u8) -> String.

Syntax

Goto has a slightly different Syntax than Go, however most syntactic elements map directly to Go or are syntactic sugar that abbreviates common patterns in Go:

Types

Collection types

Status: ⚠️ Partially Implemented

	Goto	Go
Array	[][]uint8	[][]uint8
Map	[string]uint8	map[string]uint8
Option	?string	non-existent
Result	!string	(string, error)
Nillable Pointer	*string	*string
Non-nillable Pointer	^string	non-existent
Bi-directional channel	<->string	chan string
Send-only channel	<-string	chan<- string
Receive-only channel	->string	<-chan string

Enums

Status: ⛔️ Not Implemented

Goto introduces proper enums to Go:

// season.goto

type Season enum {
        Summer = 0
	Autumn = 1
	Winter = 2
  	Spring = 3
}

type Animal enum {
	Deer
	Cat
	Dog
	Fish
}

is equivalent to

// season.go

type Season string

const (
	Summer Season = 0
	Autumn Season = 1
	Winter Season = 2
	Spring Season = 3
)

type Animal int64

const (
	Deer Animal = iota
	Cat
	Dog
	Fish
)

...but you can go further in Goto! Unlike in Go, enums cases in Goto can have associated values:

// colors.goto

type Color enum {
	// Multiple named associated values
	Colorful struct { r, g, b uint8 }
	// A single unnamed associated value
	Grayscale uint8
}

// colors.go

// TODO: We probably have to implement our own type for this to work

Strict Null-Safety

Status: ⛔️ Not Implemented

As Goto offers non-nillable pointers besides the usual Go-like pointers, nil-checks can be enforced by the compiler. Like in Go, you are explicitly encouraged to make nil a valid receiver as much as possible.

// nillsafe.goto

func doSomething(nillable *something) {
	if some := nillable; some != nil {

	}
}

Immutability by default

String interpolation

Status: ✅ Implemented

Goto has built-in string interpolation, so:

// apples.goto

func apples(count int) -> string {
	return "You have \(count:d) apples!"
}

is equivalent to

// apples.go

import "fmt"

func apples(count int) -> string {
	return fmt.Sprintf("You have %d apples!", count)
}

Goto string interpolation supports all formatting 'verbs' mentioned in the "fmt" module documentation. If no formatting verb is given, Goto defaults to :v, so the above example can be written as:

// apples.goto

func apples(count int) -> string {
	return "You have \(count) apples!"
}

Error handling

Returning an error

Status: 🚧 Work In Progress

Goto has an error return type: Just add ! after the type annotation of a return type. You can return a new error using the throw keyword:

// hello.goto

func Hello(name string) !string {
	if name == "" {
		throw "empty name"
	}

	message := "Hi, \(name:v). Welcome!"
	return message
}

is equivalent to

// hello.go

func Hello(name string) (string, error) {
	if name == "" {
		return "", errors.New("empty name")
	}

	message := fmt.Sprintf("Hi, %v. Welcome!", name)
	return message, nil
}

Note that Goto is a bit stricter when it comes to discarding return values: If a function has a return value, a call to it cannot be used as a statement - so discarding the return value(s) is only allowed explicitly.

Propagating Errors

Status: ⛔️ Not Implemented

Goto uses prefix try for error propagation:

// hello2.goto

func Hello2(name string) !string {
	greeting := try Hello(name)
	return "\(greeting), have a nice day!"
}

This is the same as try in Zig and postfix ? in Rust. While a postfix operator would be more chainable, a prefix keyword makes the control flow more clearly visible -- therefore better matching the spirit of Go.

is equivalent to

// hello2.go

func Hello2(name string) (string, error) {
	greeting, err := Hello(name)
	if err != nil {
		return "", err
	}
	return fmt.Sprintf("%v, have a nice day!", v)
}

Operator Overloading

Status: ⛔️ Not Implemented TODO: Read Go proposal on operator overloading (golang/go#27605)

Go Expression

Status: ⛔️ Not Implemented

In Goto, the go keyword can be used as an expression. It returns a channel-like 'state' for each return value of the original function. A 'state' object blocks when receiving before its value was written and returns its inner value on all subsequent receives without blocking.

// shopping.goto

func loadItems() -> []Item {
	// Under the hood, the returned value is not a channel but a 'state' that returns the last received value
	items, discounts := go fetchOffers()
	// blocks until items received a value
	for _, item := range <-items {
		print(item)
	}

	// instantly evaluates as discounts and items would be tied together
	if len(<-discounts) == 0 {
		print("No discounts!")
	}

	// instantly returns the stored value as items was already received before
	return <-items
}

is equivalent to the following Go code:

// shopping.go

func loadItems() -> []Item {
	// Under the hood, the returned value is not a channel but a 'state' that returns the last received value
	var items State[[]Item]
	var discounts State[[]Discount]
	go func() {
		items, itemsChannel = state.New()
		discounts, discountsChannel = state.New()
		i, d := fetchOffers()
		itemsChannel <- i
		discountsChannel <- d
	}()

	// blocks until items received a value
	for _, item := range items.Read() {
		print(item)
	}

	// instantly evaluates as discounts and items would be tied together
	if len(discounts.Read()) == 0 {
		print("No discounts!")
	}

	// instantly returns the stored value as items was already received before
	return items.Read()
}

TODO: The internal compiler structure for a state could look like this:

Note: This relies on the sender to only ever send one value. This is okay if we only use this as compiler intrinsics for go expressions

// state.go

type State[T any] struct {
	inner    T
	source   <-chan T
	once     Once
}

func New[T any]() -> (State[T], chan<- T) {
	channel := make(chan T, 1)
	state := State{source: channel}
	return state, channel
}

func (st *State[T]) Read[T any]() -> T {
	st.once.Do(func() { st.inner = <-st.source })

	return st.inner
}

Mascot

Goto's mascot is an orange gopher. It is a fan-modified illustration, the unmodified version was created by Takuya Ueda (https://twitter.com/tenntenn) and was obtained under the Creative Commons 3.0 Attributions license (https://creativecommons.org/licenses/by/3.0/deed.en). The original Go gopher was designed by Renee French. (http://reneefrench.blogspot.com/)

goto-lang/goto-spec

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