6. Functions and Value Flow

Lash functions lower to Bash functions, but parameter binding and return values are more structured.

Declaring and calling functions

fn greet(name, prefix = "hello")
    return $"{prefix}, {name}"
end

let message = greet("world")
echo $"{message}"

Function arity is checked. Parameters with default values are optional. Required parameters must be passed by the caller.

Return values

return expr does not lower to Bash return <number>. It emits the expression with echo, then returns status 0.

fn archive_name(name)
    return name + ".tar.gz"
end

This makes Lash functions usable in value expressions because Bash captures command output from functions.

Use bare return when you only want to stop the function successfully.

Function arguments

Arguments are rendered as shell arguments. Strings are quoted for the generated Bash.

fn show(value)
    echo $"{value}"
end

show("hello world")

Passing argv forwards all script arguments:

fn forward()
    printf '%s\n' "$@"
end

forward(argv)

Array-like parameters

When the compiler sees an array argument for a function parameter, it can lower that parameter as an array in the generated function body.

fn print_all(items)
    for item in items
        echo $"{item}"
    end
end

let names = ["a", "b"]
print_all(names)

Value pipes

fn suffix(value, ext)
    return value + ext
end

let archive = "Lash-linux-x64" | suffix(".tar.gz")

In a value pipe, the left value becomes the first argument to the function call on the right.

Unknown shell-derived values

Captures such as $(...) often produce unknown values because Bash decides the runtime output. Use explicit checks and conversions where the meaning matters.