// The outside world: files, command-line arguments, and the three standard
// streams. Everything that can fail hands the failure back as a value.
// args() gives the command line, the program itself first.
let argv = args()
print("this program is:", argv[0])
print("it received", length(argv) - 1, "argument(s) after its name")
// writeFile can fail, so it returns Result. Success carries nothing — Unit —
// but you still confirm it worked.
let path = "/tmp/lux-io-demo.txt"
match writeFile(path, "hello from lux\nsecond line\n") {
ok(let _) => print("wrote", path)
err(let e) => eprint("write failed:", e)
}
// readFile can fail too — the file might not be there. match makes you handle it.
match readFile(path) {
ok(let text) => print("read it back, length", length(text))
err(let e) => eprint("read failed:", e)
}
// Reading a file that isn't there takes the err arm instead of crashing.
match readFile("/tmp/does-not-exist-xyz.txt") {
ok(let text) => print("unexpected:", length(text))
err(let e) => eprint("expected miss:", e)
}
// readLine gives one line, or none at end of input. A loop over it reads the
// same whether a person is typing or a file is piped in. Used as an expression,
// the match yields whether to keep going — the loop condition is just data.
func echo(line: string) -> bool {
print(" >", line)
return true
}
print("echoing stdin until end of input:")
var reading = true
while reading {
reading = match readLine() {
some(let line) => echo(line)
none => false
}
}
print("done")