Guide

Command-line tools

Since Sprint 23, programs read their arguments and environment — render pipelines become real CLI tools.

fn main(sys: Env) -> Void:
    let a = args()
    if a.len() != 2:
        print("usage: ptc run tool.pt <input> <output>")
        return
    let mode = sys.var("TOOL_MODE")
    print("rendering {a[0]} to {a[1]} (mode: {mode})")

args() -> List[Text] holds everything after the file on the ptc run command line — no argv[0] to skip, no separate count, and main keeps its single canonical shape. Reading the environment is the Env capability (spec §29): take an Env in main and call sys.var(name) -> Option[Text]; unset is None, never an error. The old ambient env(name) builtin is retired — a capability makes the effect visible in the signature.