diff options
| -rw-r--r-- | src/libexpr/primops.cc | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index db7aa9e899..aa27df6ada 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -880,7 +880,8 @@ static void prim_head(EvalState & state, Value * * args, Value & v) /* Return a list consisting of everything but the the first element of - a list. */ + a list. Warning: this function takes O(n) time, so you probably + don't want to use it! */ static void prim_tail(EvalState & state, Value * * args, Value & v) { state.forceList(*args[0]); @@ -930,6 +931,19 @@ static void prim_filter(EvalState & state, Value * * args, Value & v) } +static void prim_elem(EvalState & state, Value * * args, Value & v) +{ + bool res = false; + state.forceList(*args[1]); + for (unsigned int n = 0; n < args[1]->list.length; ++n) + if (state.eqValues(*args[0], *args[1]->list.elems[n])) { + res = true; + break; + } + mkBool(v, res); +} + + /* Return the length of a list. This is an O(1) time operation. */ static void prim_length(EvalState & state, Value * * args, Value & v) { @@ -1145,8 +1159,9 @@ void EvalState::createBaseEnv() addPrimOp("__tail", 1, prim_tail); addPrimOp("map", 2, prim_map); addPrimOp("__filter", 2, prim_filter); + addPrimOp("__elem", 2, prim_elem); addPrimOp("__length", 1, prim_length); - + // Integer arithmetic addPrimOp("__add", 2, prim_add); addPrimOp("__sub", 2, prim_sub); |