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Make lists be comparable
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Makes lists comparable using lexicographic comparison.

Increments builtins.langVersion in order for this change to be
detectable
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@infinisil
infinisil committed Nov 24, 2021
1 parent 720ed47 commit 09471d2
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Showing 5 changed files with 41 additions and 11 deletions.
8 changes: 4 additions & 4 deletions doc/manual/src/expressions/language-operators.md
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Expand Up @@ -17,10 +17,10 @@ order of precedence (from strongest to weakest binding).
| String Concatenation | *string1* `+` *string2* | left | String concatenation. | 7 |
| Not | `!` *e* | none | Boolean negation. | 8 |
| Update | *e1* `//` *e2* | right | Return a set consisting of the attributes in *e1* and *e2* (with the latter taking precedence over the former in case of equally named attributes). | 9 |
| Less Than | *e1* `<` *e2*, | none | Arithmetic comparison. | 10 |
| Less Than or Equal To | *e1* `<=` *e2* | none | Arithmetic comparison. | 10 |
| Greater Than | *e1* `>` *e2* | none | Arithmetic comparison. | 10 |
| Greater Than or Equal To | *e1* `>=` *e2* | none | Arithmetic comparison. | 10 |
| Less Than | *e1* `<` *e2*, | none | Arithmetic/lexicographic comparison. | 10 |
| Less Than or Equal To | *e1* `<=` *e2* | none | Arithmetic/lexicographic comparison. | 10 |
| Greater Than | *e1* `>` *e2* | none | Arithmetic/lexicographic comparison. | 10 |
| Greater Than or Equal To | *e1* `>=` *e2* | none | Arithmetic/lexicographic comparison. | 10 |
| Equality | *e1* `==` *e2* | none | Equality. | 11 |
| Inequality | *e1* `!=` *e2* | none | Inequality. | 11 |
| Logical AND | *e1* `&&` *e2* | left | Logical AND. | 12 |
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2 changes: 2 additions & 0 deletions doc/manual/src/release-notes/rl-next.md
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Expand Up @@ -3,3 +3,5 @@
* Binary cache stores now have a setting `compression-level`.

* `nix develop` now has a flag `--unpack` to run `unpackPhase`.

* Lists can now be compared lexicographically using the `<` operator.
26 changes: 21 additions & 5 deletions src/libexpr/primops.cc
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Expand Up @@ -517,7 +517,11 @@ static RegisterPrimOp primop_isPath({

struct CompareValues
{
bool operator () (const Value * v1, const Value * v2) const
EvalState & state;

CompareValues(EvalState & state) : state(state) { };

bool operator () (Value * v1, Value * v2) const
{
if (v1->type() == nFloat && v2->type() == nInt)
return v1->fpoint < v2->integer;
Expand All @@ -534,6 +538,17 @@ struct CompareValues
return strcmp(v1->string.s, v2->string.s) < 0;
case nPath:
return strcmp(v1->path, v2->path) < 0;
case nList:
// Lexicographic comparison
for (size_t i = 0;; i++) {
if (i == v2->listSize()) {
return false;
} else if (i == v1->listSize()) {
return true;
} else if (!state.eqValues(*v1->listElems()[i], *v2->listElems()[i])) {
return (*this)(v1->listElems()[i], v2->listElems()[i]);
}
}
default:
throw EvalError("cannot compare %1% with %2%", showType(*v1), showType(*v2));
}
Expand Down Expand Up @@ -621,7 +636,8 @@ static void prim_genericClosure(EvalState & state, const Pos & pos, Value * * ar
ValueList res;
// `doneKeys' doesn't need to be a GC root, because its values are
// reachable from res.
set<Value *, CompareValues> doneKeys;
auto cmp = CompareValues(state);
set<Value *, decltype(cmp)> doneKeys(cmp);
while (!workSet.empty()) {
Value * e = *(workSet.begin());
workSet.pop_front();
Expand Down Expand Up @@ -2821,7 +2837,7 @@ static void prim_sort(EvalState & state, const Pos & pos, Value * * args, Value
/* Optimization: if the comparator is lessThan, bypass
callFunction. */
if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
return CompareValues()(a, b);
return CompareValues(state)(a, b);

Value * vs[] = {a, b};
Value vBool;
Expand Down Expand Up @@ -3103,7 +3119,7 @@ static void prim_lessThan(EvalState & state, const Pos & pos, Value * * args, Va
{
state.forceValue(*args[0], pos);
state.forceValue(*args[1], pos);
CompareValues comp;
CompareValues comp{state};
mkBool(v, comp(args[0], args[1]));
}

Expand Down Expand Up @@ -3693,7 +3709,7 @@ void EvalState::createBaseEnv()
language feature gets added. It's not necessary to increase it
when primops get added, because you can just use `builtins ?
primOp' to check. */
mkInt(v, 5);
mkInt(v, 6);
addConstant("__langVersion", v);

// Miscellaneous
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2 changes: 1 addition & 1 deletion tests/lang/eval-okay-sort.exp
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@@ -1 +1 @@
[ [ 42 77 147 249 483 526 ] [ 526 483 249 147 77 42 ] [ "bar" "fnord" "foo" "xyzzy" ] [ { key = 1; value = "foo"; } { key = 1; value = "fnord"; } { key = 2; value = "bar"; } ] ]
[ [ 42 77 147 249 483 526 ] [ 526 483 249 147 77 42 ] [ "bar" "fnord" "foo" "xyzzy" ] [ { key = 1; value = "foo"; } { key = 1; value = "fnord"; } { key = 2; value = "bar"; } ] [ [ ] [ ] [ 1 ] [ 1 4 ] [ 1 5 ] [ 1 6 ] [ 2 ] [ 2 3 ] [ 3 ] [ 3 ] ] ]
14 changes: 13 additions & 1 deletion tests/lang/eval-okay-sort.nix
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Expand Up @@ -4,5 +4,17 @@ with builtins;
(sort (x: y: y < x) [ 483 249 526 147 42 77 ])
(sort lessThan [ "foo" "bar" "xyzzy" "fnord" ])
(sort (x: y: x.key < y.key)
[ { key = 1; value = "foo"; } { key = 2; value = "bar"; } { key = 1; value = "fnord"; } ])
[ { key = 1; value = "foo"; } { key = 2; value = "bar"; } { key = 1; value = "fnord"; } ])
(sort lessThan [
[ 1 6 ]
[ ]
[ 2 3 ]
[ 3 ]
[ 1 5 ]
[ 2 ]
[ 1 ]
[ ]
[ 1 4 ]
[ 3 ]
])
]

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