map

builtins.map

Primop

Docs pulled from | This Revision | about 11 hours ago

Nix manual

Takes 2 arguments

f, list

Apply the function f to each element in the list list. For example,

map (x: "foo" + x) [ "bar" "bla" "abc" ]

evaluates to [ "foobar" "foobla" "fooabc" ].

Time Complexity

O(n) where:

n = list length

Calls to f are performed afterwards when needed.

Noogle detected

Aliases

Detected Type

map :: (a -> b) -> [a] -> [b]

Implementation

This function is implemented in c++ and is part of the native nix runtime.

src/libexpr/primops.cc:3812

static void prim_map(EvalState & state, const PosIdx pos, Value ** args, Value & v)
{
    state.forceList(*args[1], pos, "while evaluating the second argument passed to builtins.map");

    if (args[1]->listSize() == 0) {
        v = *args[1];
        return;
    }

    state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.map");

    auto list = state.buildList(args[1]->listSize());
    for (const auto & [n, v] : enumerate(list))
        (v = state.allocValue())->mkApp(args[0], args[1]->listView()[n]);
    v.mkList(list);
}