## Lists

## Usage

    list(...)
    as.list(x)
    is.list(x)
    alist(...)

## Description

The arguments to `list` are of the form `value` or `tag=value`. The function returns a list composed of its arguments with each value either tagged or untagged, depending on how the argument was specified.

`alist` is like `list`, except in the handling of tagged arguments with no value. These are handled as if they described function arguments with no default (cf. `formals`), whereas `list` simply ignores them.

`as.list` attempts to coerce its argument to list type. For functions, this returns the concatenation of the list of formals arguments and the function body. For expressions, the list of constituent calls is returned.

`is.list` returns `TRUE` if its argument is a list and `FALSE` otherwise.

To create an empty list, it is necessary to use the function `vector` with a `mode` of `"list"`.

## See Also

`vector(., mode="list")`, `c`, for concatenation; `formals`.

## Examples

    data(cars)
    # create a plotting structure
    pts <- list(x=cars[,1], y=cars[,2])
    plot(pts)

    # Argument lists
    f <- function()x
    formals(f) <- alist(x=, y=2, ...=) # Note the spec. of a "..." argument
    f

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