Functions

Functions are reusable, parametrized templates. You define one with fn and a parameter list, then call it as name(args) — each call is replaced by the function body with ${param} filled in. They build on variables: a function body can use both its parameters and global @vars.

Defining and calling

fn arxiv(id, name) {
    https://arxiv.org/pdf/${id} as "${name}" !retry(3)
}

downloads {
    arxiv("2203.08877", "paper1.pdf")
    arxiv("2405.01513", "paper2.pdf")
}

After expansion this is exactly:

downloads {
    https://arxiv.org/pdf/2203.08877 as "paper1.pdf" !retry(3)
    https://arxiv.org/pdf/2405.01513 as "paper2.pdf" !retry(3)
}

• Definition — fn name(p1, p2, …) { ... }. The name starts with a letter or _; the body can span multiple lines.
• Call — name("a", "b"). Arguments are comma-separated; surrounding double quotes are stripped.
• Parameters — referenced in the body with ${param}, the same syntax as variables.

Combining with variables

A function body and its arguments can reference global variables:

@var gist "https://gist.githubusercontent.com/Kremilly"

fn doc(path, name) {
    ${gist}/${path} as "${name}"
}

downloads {
    doc("abc123/file.tex", "file.pdf")
}

Functions are expanded first, then variables — so the ${gist} left behind by the call is resolved afterwards.

Notes

• fn definitions are removed after expansion, so they don't affect downloads, validation or the served source.
• Functions may call other functions; expansion repeats until stable (bounded, so a self-referential definition can't loop forever).
• A call to an undefined function (e.g. missing(...)) is left untouched, making typos easy to spot.
• A missing argument expands to an empty string.