3. Arguments and absence

The program needs a file path. Accept an array of command-line arguments and use a nullable result when exactly one argument is not available.

Replace App.kalm:

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fun requestedPath(args: Array<Text>) -> Text?:
    if len(args) == 1:
        return args[0]
    return null

pub fun main(args: Array<Text>) -> Unit:
    fix requested = requestedPath(args)
    if requested != null:
        sayLine(@"Will read $requested")
    else:
        sayLine("Usage: kalm run -- <file>")

Text? can contain text or null. Checking a stable fix binding refines it inside the non-null branch. Checking the argument count first also avoids an out-of-bounds access.

kalm run -- notes.txt

Will read notes.txt

Run without an argument to see the usage message. Nothing reads the file yet. The -- separates CLI options from your program's arguments.