Removing Unsafe.set_atom_field (#4023)

Introducing `Meta.atom_with_hole` to create an `Atom` _with a hole_ that is then _safely_ filled in later.

CHANGELOG.md

@@ -498,6 +498,7 @@
 - [IGV can jump to JMH sources & more][4008]
 - [Basic support of VSCode integration][4014]
 - [Sync language server with file system after VCS restore][4020]
+- [Introducing Meta.atom_with_hole][4023]
 - [Report failures in name resolution in type signatures][4030]
 
 [3227]: https://github.com/enso-org/enso/pull/3227
@@ -580,6 +581,7 @@
 [4008]: https://github.com/enso-org/enso/pull/4008
 [4014]: https://github.com/enso-org/enso/pull/4014
 [4020]: https://github.com/enso-org/enso/pull/4020
+[4023]: https://github.com/enso-org/enso/pull/4023
 [4030]: https://github.com/enso-org/enso/pull/4030
 
 # Enso 2.0.0-alpha.18 (2021-10-12)

distribution/lib/Standard/Base/0.0.0-dev/src/Data/List.enso

@@ -7,7 +7,7 @@ import project.Data.Vector.Vector
 import project.Error.Error
 import project.Function.Function
 import project.Nothing.Nothing
-import project.Runtime.Unsafe
+import project.Meta
 
 from project.Data.Boolean import Boolean, True, False
 
@@ -185,13 +185,19 @@ type List
     filter : (Filter_Condition | (Any -> Boolean)) -> Vector Any
     filter self filter = case filter of
         _ : Filter_Condition -> self.filter filter.to_predicate
-        predicate : Function ->
-            go_filter list = case list of
-                Nil -> Nil
-                Cons h t ->
-                    rest = go_filter t
-                    if predicate h then Cons h rest else rest
-            go_filter self
+        predicate : Function -> case self of
+            Nil -> Nil
+            Cons x xs -> if predicate x . not then @Tail_Call xs.filter filter else
+                go list fill = case list of
+                    Nil -> fill Nil
+                    Cons h t -> if predicate h . not then @Tail_Call go t fill else
+                        res = Meta.atom_with_hole (Cons h _)
+                        fill res.value
+                        @Tail_Call go t res.fill
+
+                res = Meta.atom_with_hole (Cons x _)
+                go xs res.fill
+                res.value
 
     ## Applies a function to each element of the list, returning the list of
        results.
@@ -209,9 +215,18 @@ type List
     map self f = case self of
         Nil -> Nil
         Cons h t ->
-            res = Cons (f h) Nil
-            map_helper t res f
-            res
+            go : List -> Any -> (Any -> Any) -> Nothing
+            go list fill = case list of
+                Nil -> fill Nil
+                Cons h t ->
+                    v = f h
+                    res = Meta.atom_with_hole (Cons v _)
+                    fill res.value
+                    @Tail_Call go t res.fill
+            v = f h
+            res = Meta.atom_with_hole (Cons v _)
+            go t res.fill
+            res.value
 
     ## Applies a function to each element of the list.
 
@@ -281,7 +296,16 @@ type List
     take_start : Integer -> List
     take_start self count = if count <= 0 then Nil else case self of
         Nil -> Nil
-        Cons a b -> Cons a (b.take_start count-1)
+        Cons a b ->
+            go c l fill = if c <= 0 then fill Nil else case l of
+                Nil -> fill Nil
+                Cons a b ->
+                    res = Meta.atom_with_hole (Cons a _)
+                    fill res.value
+                    @Tail_Call go c-1 b res.fill
+            res = Meta.atom_with_hole (Cons a _)
+            go count-1 b res.fill
+            res.value
 
     ## Get the first element from the list.
 
@@ -319,12 +343,21 @@ type List
              example_init = Examples.list.init
     init : List ! Empty_Error
     init self =
-        init_fn x y = case y of
-            Nil -> Nil
-            Cons a b -> Cons x (init_fn a b)
         case self of
             Nil -> Error.throw Empty_Error
-            Cons a b -> init_fn a b
+            Cons _ Nil -> Nil
+            Cons a b ->
+                go l fill = case l of
+                    Cons x xs -> case xs of
+                        Nil -> fill Nil
+                        Cons _ _ ->
+                            res = Meta.atom_with_hole (Cons x _)
+                            fill res.value
+                            @Tail_Call go xs res.fill
+
+                res = Meta.atom_with_hole (Cons a _)
+                go b res.fill
+                res.value
 
     ## Get the last element of the list.
 
@@ -369,6 +402,13 @@ type List
             builder.append elem
         builder.to_vector
 
+    to_text : Text
+    to_text self =
+        go l t = case l of
+            Nil -> t + "Nil"
+            Cons x xs -> @Tail_Call go xs (t + "Cons " + x.to_text + " ")
+        go self ""
+
 ## UNSTABLE
 
    An error representing that the list is empty.
@@ -379,21 +419,3 @@ type Empty_Error
     to_display_text : Text
     to_display_text self = "The List is empty."
 
-## PRIVATE
-   A helper for the `map` function.
-
-   Arguments:
-   - list: The list to map over.
-   - cons: The current field to set.
-   - f: The function to apply to the value.
-
-   Uses unsafe field mutation under the hood, to rewrite `map` in
-   a tail-recursive manner. The mutation is purely internal and does not leak
-   to the user-facing API.
-map_helper : List -> Any -> (Any -> Any) -> Nothing
-map_helper list cons f = case list of
-    Nil -> Unsafe.set_atom_field cons 1 Nil
-    Cons h t ->
-        res = Cons (f h) Nil
-        Unsafe.set_atom_field cons 1 res
-        @Tail_Call map_helper t res f

distribution/lib/Standard/Base/0.0.0-dev/src/Meta.enso

@@ -273,6 +273,17 @@ get_constructor_name atom_constructor = @Builtin_Method "Meta.get_constructor_na
 new_atom : Any -> Array -> Atom
 new_atom constructor fields = @Builtin_Method "Meta.new_atom"
 
+## PRIVATE
+
+   Constructs a new atom with a "hole". Returns an object with `value` and
+   `fill` properties. Value contains the created atom and `fill` holds a
+   function to "fill the hole" later.
+
+   Arguments:
+   - factory: a function that takes the "hole" element and returns newly created atom
+atom_with_hole : (Any -> Atom) -> Any
+atom_with_hole factory = @Builtin_Method "Meta.atom_with_hole_builtin"
+
 ## UNSTABLE
    ADVANCED
 

engine/runtime/src/bench/java/org/enso/interpreter/bench/benchmarks/semantic/ListBenchmarks.java

@@ -0,0 +1,107 @@
+package org.enso.interpreter.bench.benchmarks.semantic;
+
+import java.io.ByteArrayOutputStream;
+import java.nio.file.Paths;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
+import org.graalvm.polyglot.Context;
+import org.graalvm.polyglot.Value;
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Fork;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.Setup;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.infra.BenchmarkParams;
+import org.openjdk.jmh.infra.Blackhole;
+
+
+@BenchmarkMode(Mode.AverageTime)
+@Fork(1)
+@Warmup(iterations = 3)
+@Measurement(iterations = 5)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@State(Scope.Benchmark)
+public class ListBenchmarks {
+  private final int LENGTH_OF_EXPERIMENT = 1_000_000;
+  private Value list;
+  private Value plusOne;
+  private Value self;
+  private Value sum;
+  private Value oldSum;
+
+  @Setup
+  public void initializeBenchmark(BenchmarkParams params) throws Exception {
+    var ctx = Context.newBuilder()
+      .allowExperimentalOptions(true)
+      .allowIO(true)
+      .allowAllAccess(true)
+      .logHandler(new ByteArrayOutputStream())
+      .option(
+        "enso.languageHomeOverride",
+        Paths.get("../../distribution/component").toFile().getAbsolutePath()
+      ).build();
+
+    var benchmarkName = params.getBenchmark().replaceFirst(".*\\.", "");
+    var code = """
+      from Standard.Base.Data.List.List import Cons, Nil
+      import Standard.Base.IO
+
+      plus_one list = list.map (x -> x + 1)
+
+      sum list acc =
+          case list of
+              Nil -> acc
+              Cons x xs -> @Tail_Call sum xs acc+x
+
+      generator n =
+          go x v l = if x > n then l else
+              @Tail_Call go x+1 v+1 (Cons v l)
+          go 1 1 Nil
+      """;
+
+    var module = ctx.eval(SrcUtil.source(benchmarkName, code));
+
+    this.self = module.invokeMember("get_associated_type");
+    Function<String,Value> getMethod = (name) -> module.invokeMember("get_method", self, name);
+
+    Value longList = getMethod.apply("generator").execute(self, LENGTH_OF_EXPERIMENT);
+
+    this.plusOne = getMethod.apply("plus_one");
+    this.sum = getMethod.apply("sum");
+
+    switch (benchmarkName) {
+      case "mapOverList": {
+        this.list = longList;
+        this.oldSum = sum.execute(self, longList, 0);
+        if (!this.oldSum.fitsInLong()) {
+          throw new AssertionError("Expecting a number " + this.oldSum);
+        }
+        break;
+      }
+      default:
+        throw new IllegalStateException("Unexpected benchmark: " + params.getBenchmark());
+    }
+  }
+
+  @Benchmark
+  public void mapOverList(Blackhole matter) {
+    performBenchmark(matter);
+  }
+
+  private void performBenchmark(Blackhole hole) throws AssertionError {
+    var newList = plusOne.execute(self, list);
+    var newSum = sum.execute(self, newList, 0);
+
+    var result = newSum.asLong() - oldSum.asLong();
+    if (result != LENGTH_OF_EXPERIMENT) {
+      throw new AssertionError("Unexpected result " + result);
+    }
+    hole.consume(result);
+  }
+}
+

engine/runtime/src/bench/java/org/enso/interpreter/bench/benchmarks/semantic/VectorBenchmarks.java

@@ -1,4 +1,4 @@
-    package org.enso.interpreter.bench.benchmarks.semantic;
+package org.enso.interpreter.bench.benchmarks.semantic;
 
 import java.io.ByteArrayOutputStream;
 import java.nio.file.Paths;