mirror of
https://github.com/enso-org/enso.git
synced 2024-12-27 02:12:05 +03:00
190 lines
6.9 KiB
Markdown
190 lines
6.9 KiB
Markdown
---
|
|
layout: developer-doc
|
|
title: Polyglot Bindings
|
|
category: polyglot
|
|
tags: [polyglot, bindings, interop]
|
|
order: 1
|
|
---
|
|
|
|
# Polyglot Bindings
|
|
|
|
This document deals with the specification and design for the polyglot interop
|
|
system provided in the Enso runtime. This system allows users to connect Enso to
|
|
other supported programming languages, to both provide access to a wealth of
|
|
libraries, and to integrate Enso into existing systems.
|
|
|
|
The polyglot support in Enso is best-in class, and it supports this through two
|
|
main mechanisms:
|
|
|
|
1. **Polyglot FFI:** The low-level polyglot support provides a fairly low-level
|
|
syntax sugar system for working with values from foreign languages.
|
|
2. **Embedded Syntax:** This system allows users to write code from other
|
|
languages directly in their `.enso` files, and to seamlessly share values
|
|
between Enso and that foreign code.
|
|
|
|
<!-- MarkdownTOC levels="2,3" autolink="true" -->
|
|
|
|
- [Impedance Mismatch](#impedance-mismatch)
|
|
- [The Polyglot FFI](#the-polyglot-ffi)
|
|
- [Importing Polyglot Bindings](#importing-polyglot-bindings)
|
|
- [Using Polyglot Bindings](#using-polyglot-bindings)
|
|
- [Importing Polyglot Bindings \(Syntax\)](#importing-polyglot-bindings-syntax)
|
|
- [Using Polyglot Bindings \(Syntax\)](#using-polyglot-bindings-syntax)
|
|
- [Finding Polyglot Bindings](#finding-polyglot-bindings)
|
|
- [Embedded Syntax](#embedded-syntax)
|
|
- [Embedded Syntax Usage \(Syntax\)](#embedded-syntax-usage-syntax)
|
|
|
|
<!-- /MarkdownTOC -->
|
|
|
|
## Impedance Mismatch
|
|
|
|
Polyglot interoperation in Enso has a significant impedance mismatch. In
|
|
essence, this means that there is a mismatch between Enso's language semantics
|
|
and the semantics of the foreign languages that are being worked with.
|
|
|
|
While some of this mismatch can be worked around by manually wrapping the
|
|
foreign constructs in Enso, there are still concepts that can't easily be
|
|
represented by Enso.
|
|
|
|
> The actionables for this section are:
|
|
>
|
|
> - Expand on the impedance mismatch and how it leads to the defined semantics.
|
|
|
|
## The Polyglot FFI
|
|
|
|
The low-level polyglot FFI mechanism refers to a way to use polyglot objects
|
|
directly in Enso code. This can be used to underlie a library implementaion in
|
|
Enso, or to interoperate with code running in other languages.
|
|
|
|
The mechanism provides users with the facilities to import bindings from other
|
|
languages and call them via a generic mechanism.
|
|
|
|
### Importing Polyglot Bindings
|
|
|
|
When importing a polyglot binding into scope in an Enso file, this introduces a
|
|
_polyglot object_ into scope. This object will have appropriate fields and/or
|
|
methods defined on it, as described by the foreign language implementation.
|
|
|
|
> The actionables for this section are:
|
|
>
|
|
> - Expand greatly on the detail of this as the semantics of the imports become
|
|
> clearer.
|
|
|
|
### Using Polyglot Bindings
|
|
|
|
With a polyglot object in scope, the user is free to call methods on it
|
|
directly. These polyglot objects are inherently dynamically typed, meaning that
|
|
any operation may _fail_ at runtime.
|
|
|
|
Enso implements a generic variadic syntax for calling polyglot functions using
|
|
vectors of arguments. In essence, this is necessary due to the significant
|
|
impedance mismatch between Enso's runtime semantics (let alone the type system)
|
|
and the runtime semantics of many of the polyglot languages.
|
|
|
|
We went the way of the variadic call for multiple reasons:
|
|
|
|
- It allows us to match up with a wide range of language semantics (such as
|
|
subtyping and overloading).
|
|
- It is flexible and easy to expand in the future.
|
|
- We can easily build a more Enso-feeling interface on top of it.
|
|
|
|
By way of illustrative example, Java supports method overloading and subtyping,
|
|
two things which have no real equivalent in the Enso type system.
|
|
|
|
> The actionables for this section are:
|
|
>
|
|
> - Expand greatly on the runtime semantics of working with polyglot bindings.
|
|
> - Determine how to make the inherent 'failability' of polyglot objects safer.
|
|
|
|
### Importing Polyglot Bindings (Syntax)
|
|
|
|
Polyglot bindings can be imported using a polyglot import directive. This is
|
|
constructed as follows:
|
|
|
|
- The `polyglot` keyword
|
|
- A language identifier (e.g. `java`).
|
|
- The keyword `import`.
|
|
- Optionally (where the language supports it), an identifier for the type of
|
|
language entity being imported (e.g. `struct` for `c`).
|
|
- A path that uniquely identifies the polyglot object to import.
|
|
- Optionally, the keyword `as`, followed by a new name.
|
|
|
|
For example:
|
|
|
|
```ruby
|
|
polyglot java import org.example.MyClass as MyClassJava
|
|
polyglot c import struct NetworkPacket as NetworkPacketC
|
|
```
|
|
|
|
### Using Polyglot Bindings (Syntax)
|
|
|
|
A polyglot binding is a polyglot object that has methods and/or fields defined
|
|
on it. Due to an impedance mismatch between languages, Enso implements a
|
|
variadic syntax for calling these polyglot bindings using vectors.
|
|
|
|
In essence, we have a primitive function as follows:
|
|
|
|
```ruby
|
|
Polyglot.method : Polyglot.Object -> [Any] -> Any
|
|
```
|
|
|
|
It works as follows:
|
|
|
|
- It is a method called `method` defined on the `Polyglot` type. The name
|
|
`method` is, however, a stand-in for the name of the method in question.
|
|
- It takes an object instance of the polyglot object.
|
|
- It takes a vector of arguments (and is hence variadic).
|
|
- And it returns some value.
|
|
|
|
By way of example, the following is a valid usage of a polyglot binding:
|
|
|
|
```ruby
|
|
polyglot java import com.example.MyClass as MyClassJava
|
|
|
|
main =
|
|
x = MyClassJava.foo [1, 2, 3] # a static method
|
|
inst = MyClassJava.new [a, b, c] # a constructor
|
|
bar = inst.metod [x, y] # a static method
|
|
```
|
|
|
|
### Finding Polyglot Bindings
|
|
|
|
Polyglot objects for various languages are found in the `polyglot` subdirectory
|
|
of an Enso project. This folder is subdivided into directories based on the
|
|
polyglot language. The name of each subdirectory must match the language
|
|
identifier used in the source code.
|
|
|
|
Inside each directory is an implementation-defined structure, with the polyglot
|
|
implementation for that particular language needing to specify it. Please see
|
|
the language-specific documentation for details.
|
|
|
|
## Embedded Syntax
|
|
|
|
The term "Embedded Syntax" is our terminology for the ability to use foreign
|
|
language syntaxes from directly inside `.enso` files. This system builds upon
|
|
the more generic mechanisms used by the [polyglot FFI](#the-polyglot-ffi) to
|
|
provide a truly seamless user experience.
|
|
|
|
### Embedded Syntax Usage (Syntax)
|
|
|
|
A polyglot block is introduced as follows:
|
|
|
|
- The `polyglot` keyword starts a block.
|
|
- This must be followed by a language identifier (e.g. `java`).
|
|
- After the language identifier, the remaining syntax behaves like it is an Enso
|
|
function definition until the `=`.
|
|
- After the `=`, the user may write their foreign code.
|
|
|
|
```ruby
|
|
polyglot python concat a b =
|
|
def concat(a, b):
|
|
str(a) + str(b)
|
|
```
|
|
|
|
In the above example, this defines a function `concat` that takes two arguments
|
|
`a` and `b`, implemented in Python.
|
|
|
|
> The actionables for this section are:
|
|
>
|
|
> - Greatly flesh out the syntax for the high-level polyglot functionality.
|