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Add a primop ‘concatLists’

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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
This commit is contained in:
Eelco Dolstra 2012-08-13 01:53:10 -04:00
parent b9e5b908ed
commit 198d0338be
3 changed files with 33 additions and 8 deletions
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10
src/libexpr/primops.cc
View file

@ -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