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author | Eelco Dolstra <eelco.dolstra@logicblox.com> | 2012-08-13T05·53-0400 |
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committer | Eelco Dolstra <eelco.dolstra@logicblox.com> | 2012-08-13T05·53-0400 |
commit | 198d0338be7c105b6dbd707f98e0c223a8358240 (patch) | |
tree | 60653ffc15a4579bd21fa1057abe7cdefaa94d89 /src/libexpr/primops.cc | |
parent | b9e5b908ed29bfb6cd82837f9f57293c1f63e999 (diff) |
Add a primop ‘concatLists’
This can serve as a generic efficient list builder. For instance, the function ‘catAttrs’ in Nixpkgs can be rewritten from attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l to attr: l: builtins.concatLists (map (s: if hasAttr attr s then [(getAttr attr s)] else []) l) Statistics before: time elapsed: 1.08683 size of a value: 24 environments allocated: 1384376 (35809568 bytes) list elements: 6946783 (55574264 bytes) list concatenations: 37434 values allocated: 1760440 (42250560 bytes) attribute sets allocated: 392040 right-biased unions: 186334 values copied in right-biased unions: 591137 symbols in symbol table: 18273 number of thunks: 1297673 number of thunks avoided: 1380759 number of attr lookups: 430802 number of primop calls: 628912 number of function calls: 1333544 Statistics after (including new catAttrs): time elapsed: 0.959854 size of a value: 24 environments allocated: 1010198 (26829296 bytes) list elements: 1984878 (15879024 bytes) list concatenations: 30488 values allocated: 1589760 (38154240 bytes) attribute sets allocated: 392040 right-biased unions: 186334 values copied in right-biased unions: 591137 symbols in symbol table: 18274 number of thunks: 1040925 number of thunks avoided: 1038428 number of attr lookups: 438419 number of primop calls: 474844 number of function calls: 959366
Diffstat (limited to '')
-rw-r--r-- | src/libexpr/primops.cc | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc index aa27df6ada11..f5c004044135 100644 --- a/src/libexpr/primops.cc +++ b/src/libexpr/primops.cc @@ -931,6 +931,7 @@ static void prim_filter(EvalState & state, Value * * args, Value & v) } +/* Return true if a list contains a given element. */ static void prim_elem(EvalState & state, Value * * args, Value & v) { bool res = false; @@ -944,6 +945,14 @@ static void prim_elem(EvalState & state, Value * * args, Value & v) } +/* Concatenate a list of lists. */ +static void prim_concatLists(EvalState & state, Value * * args, Value & v) +{ + state.forceList(*args[0]); + state.concatLists(v, args[0]->list.length, args[0]->list.elems); +} + + /* Return the length of a list. This is an O(1) time operation. */ static void prim_length(EvalState & state, Value * * args, Value & v) { @@ -1160,6 +1169,7 @@ void EvalState::createBaseEnv() addPrimOp("map", 2, prim_map); addPrimOp("__filter", 2, prim_filter); addPrimOp("__elem", 2, prim_elem); + addPrimOp("__concatLists", 1, prim_concatLists); addPrimOp("__length", 1, prim_length); // Integer arithmetic |