diff options
| -rw-r--r-- | doc/manual/expressions/builtins.xml | 18 | ||||
| -rw-r--r-- | src/libexpr/primops.cc | 20 | ||||
| -rw-r--r-- | tests/lang/lib.nix | 6 |
3 files changed, 41 insertions, 3 deletions
diff --git a/doc/manual/expressions/builtins.xml b/doc/manual/expressions/builtins.xml index 099f90e786e5..4461570565e1 100644 --- a/doc/manual/expressions/builtins.xml +++ b/doc/manual/expressions/builtins.xml @@ -364,6 +364,24 @@ builtins.fromJSON ''{"x": [1, 2, 3], "y": null}'' </varlistentry> + <varlistentry><term><function>builtins.genList</function> + <replaceable>generator</replaceable> <replaceable>length</replaceable></term> + + <listitem><para>Generate list of size + <replaceable>length</replaceable>, with each element + <replaceable>i></replaceable> equal to the value returned by + <replaceable>generator</replaceable> <literal>i</literal>. For + example, + +<programlisting> +builtins.genList (x: x * x) 5 +</programlisting> + + returns the list <literal>[ 0 1 4 9 16 ]</literal>.</para></listitem> + + </varlistentry> + + <varlistentry><term><function>builtins.getAttr</function> <replaceable>s</replaceable> <replaceable>set</replaceable></term> diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index ece76975d034..5da2f3463570 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -1364,6 +1364,25 @@ static void prim_all(EvalState & state, const Pos & pos, Value * * args, Value & } +/* Apply a function to every element of a list. */ +static void prim_genList(EvalState & state, const Pos & pos, Value * * args, Value & v) +{ + state.forceFunction(*args[0], pos); + auto len = state.forceInt(*args[1], pos); + + if (len < 0) + throw EvalError(format("cannot create list of size %1%, at %2%") % len % pos); + + state.mkList(v, len); + + for (unsigned int n = 0; n < len; ++n) { + Value * arg = state.allocValue(); + mkInt(*arg, n); + mkApp(*(v.listElems()[n] = state.allocValue()), *args[0], *arg); + } +} + + /************************************************************* * Integer arithmetic *************************************************************/ @@ -1759,6 +1778,7 @@ void EvalState::createBaseEnv() addPrimOp("__foldl'", 3, prim_foldlStrict); addPrimOp("__any", 2, prim_any); addPrimOp("__all", 2, prim_all); + addPrimOp("__genList", 2, prim_genList); // Integer arithmetic addPrimOp("__add", 2, prim_add); diff --git a/tests/lang/lib.nix b/tests/lang/lib.nix index 262cdd7e8fd0..028a538314b7 100644 --- a/tests/lang/lib.nix +++ b/tests/lang/lib.nix @@ -54,8 +54,8 @@ rec { const = x: y: x; range = first: last: - if builtins.lessThan last first - then [] - else [first] ++ range (builtins.add first 1) last; + if first > last + then [] + else genList (n: first + n) (last - first + 1); } |