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Release v1.4.0

Release v1.4.0

Risor v1.4.0 is here! This release includes several interesting new features that you also might find familiar if you know Go. For anyone new to Risor, it's a scripting language written in Go that interoperates well with all the existing Go libraries and its overall ecosystem.

For a quick taste, here's an example of an HTTP server one-liner using the Risor CLI:

risor -c 'http.listen_and_serve(":8085", func(w, r) { "OK" })'

New Features

This release adds support for the go and defer keywords, channels, HTTP servers, improved Risor VM cloning, CLI utilities, and range and from-import statement improvements. More details on all of this below.

New Risor Keywords

The go keyword is now supported, with a direct correspondence to the underlying capability from the Go runtime. This allows you to run Risor code concurrently. Under the hood, when go is used, the active Risor VM is cloned in order to have a separate Risor frame and data stack for the new goroutine. Since Risor VMs are lightweight, this is in-fitting with Go's own lightweight goroutines.

go func(n) {
    for i := 0; i < n; i++ {
        print("count:", i)


count: 0
count: 1
count: 2
count: 3

Similarly, there is now Risor support for the Go defer keyword, again with a fairly direct correspondence to the underlying Go feature. Multiple defer statements can be made and they are executed in reverse order when the function returns.

func() {
    defer print("world")
    defer print("hello")




Channels are now supported and are the primary means of communication between Risor goroutines. All channels are typed to Risor's object.Object type. Channel buffering is configurable as in Go, and channels can be closed. The <- operator is used to send and receive values.

As a convenience, a new channel can be created simply by calling chan() with an optional buffer size. Creation using make(chan) is also supported. Note that there is no type parameter since all channels are typed to object.Object.

Iteration over channels behaves as in Go.

ch := chan(2)
ch <- 1
ch <- 2
for _, value := range ch {

HTTP servers

Risor can now be used to run HTTP servers and it leverages the new HTTP mux behavior from the Go 1.22 release. I think this really nicely shows how Risor's concise syntax can be used to quickly put together a simple backend.

As a convenience in Risor, handler return values may be used as the response body. If the return value is a string or byte slice, it is written to the body as-is. If the return value is a map or list, it is marshaled to JSON automatically and written to the body.

Since the return statement can also be omitted in Risor, you can also just have the handler implicitly return the value of the last expression.

http.handle("/", func(w, r) {
    return "OK"
// Explicit write_header and write calls
http.handle("POST /messages", func(w, r) {
    w.write("message sent")
// Using path value feature from Go 1.22, with implicit JSON response marshaling
http.handle("/animals/{name}", func(w, r) {
    return { animal: r.path_value("name") }

CLI Apps

It was already possible to write simple CLIs in Risor, but this release adds more sophisticated support by wrapping urfave/cli (opens in a new tab).

In your Risor script, use the following shebang line to ensure that CLI args are passed correctly to the CLI app:

#!/usr/bin/env risor --

Building the CLI app then looks very similar to how you would do it in Go when using urfave/cli. Create an app, add commands and flags, then run the app.

#!/usr/bin/env risor --{
    name: "encode",
    help_name: "encode",
    description: "Encode input text using various codecs",
    commands: [
            name: "base64",
            flags: [
                    name: "verbose",
                    aliases: ["v"],
                    usage: "Print verbose output",
                    env_vars: ["VERBOSE"],
                    value: false,
            action: func(ctx) {
                if ctx.bool("verbose") {
                    // yadda yadda
                for _, text := range ctx.args() {
                    print(encode(text, "base64"))

Range Over Integers

The range statement now supports ranging over integers, as is now available in Go 1.22:

for i := range 5 {

Note that Risor is a bit more flexible with range statements than Go, since Risor's range statement can be used with any object that implements the Risor object.Iterable interface. That's why all these examples work in Risor:

for i := range [1, 2, 3] {
for i, s := range "hello" {
    print(i, s)
it := iter(5)
for i := range it {

From-Import Improvement

The from-import statement now supports importing multiple names from a package with optional name aliasing. This is quite similar to Python's from-import behavior.

from cli import (

Wrapping Up

Thanks for reading about the new release. As usual, please drop in on the GitHub discussions (opens in a new tab) to share any feedback or ask questions.

If you're new to Risor, the quickest way to install it is using Homebrew:

brew install risor

Happy scripting!