4. Collections, Indexing, and argv

Lash arrays and maps lower to Bash arrays. The compiler tracks whether a container is numeric-indexed or string-keyed so accidental mixed indexing can be reported early.

Arrays

let items = ["alpha", "beta", "gamma"]
let count = #items

echo $"{items[0]}"
echo $"count={count}"

Numeric arrays lower to Bash indexed arrays.

Array append

+= is overloaded. With arrays, it appends array values.

var items = ["alpha"]
items += ["beta", "gamma"]

When the right-hand side looks numeric, += is arithmetic. If the compiler cannot tell which mode you intended, it reports an ambiguity.

Maps

let meta = {
    "name": "lash",
    "shell": "bash"
}

echo $"{meta["name"]}"

Maps are string-keyed containers and lower to Bash associative arrays. Map literal keys must be strings.

Do not mix numeric and string keys for the same container.

Index assignments

var items = ["a", "b"]
items[1] = "changed"

var meta = {"name": "lash"}
meta["version"] = "0.3"

Index assignment targets must be named variables. Assigning into an arbitrary expression is rejected for Bash code generation.

argv

argv represents script positional arguments.

let arg_count = #argv
echo $"{argv[0]}"
echo $"arg-count={arg_count}"

for arg in argv
    echo $"{arg}"
end

Lash uses zero-based indexing for argv[index]. Bash positional parameters are one-based, so the compiler lowers argv[0] to the first Bash argument.

Bare argv is allowed in contexts where the compiler can expand it safely, such as declarations, function arguments, for ranges, appends, and length checks.

let args = argv
items += argv

Assignment to argv is not supported.