Developers / HollowScript

HollowScript Preview

A small, statically typed, capability-based language you can embed and run. It is in Preview.

Tour, spec and install

Why it exists

Small, safe and embeddable

Statically typed

Records, closures, pattern matching, optionals and result-based errors, checked before it runs.

Capability-based

A program gets only the capabilities it is granted. Filesystem, network and the rest are off by default.

Embeddable

Compile to a verified bytecode container a host loads from Rust, C or, through WebAssembly, JavaScript.

A taste

A small program

uses print

record Task = { title: String, owner: String? }

fn ownerOf(task: Task): String {
    match task.owner {
        none { return "unassigned" }
        else { return task.owner }
    }
}

constant tasks: [Task] = [
    { title: "Fix build", owner: "sam" },
    { title: "Write docs", owner: none }
]

for task in tasks {
    effect print("${ownerOf(task)}: ${task.title}")
}

Filters

HEL, the filter language

HEL is a separate, smaller expression language for filters. It also appears inside HollowScript as backtick filter literals. Hollow uses HEL for the filters in Tasks, Search and Cascade.

In Cascade

Where you can run it today

A Cascade Code step can be written in HollowScript, which is in Preview. For the full language, tour and spec, see hollowscript.org.