filter function:

Filter a list. If the first argument is a list, return all the values for which the second argument is a list.

Examples:

• running: (filter [1, 2, 3, 4], true) will give: [1, 2, 3, 4]

• running: (filter [1, 2, 3, 4], null) will give: []

• running: (filter [1, 2, 3, 4, "one", null], (string? .)) will give: ["one"] Because only the value "one" is a string.

• running: (filter ., (.number?)) for input: [1, 2, null, "a", 4] will give: [1, 2, 4]

• running: (filter {}, true) will return nothing