From 50807f3dd5241667dac0c0cc302042d648de4b42 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Tue, 28 Jul 2015 17:27:32 +0200 Subject: Add primop genList MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This can be used to implement functions like ‘imap’ (or for that matter, ‘map’) without the quadratic complexity incurred by calling ‘++’ repeatedly. --- src/libexpr/primops.cc | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'src/libexpr') 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); -- cgit 1.4.1