Suspended atom fields are evaluated only once

[JaroslavTulach]

Pull Request Description

Implements #6134.

Important Notes

One can define lazy atom fields as:

type Lazy
    Value ~x ~y

the evaluation of the x and y fields is then delayed until they are needed. The evaluation happens once. Then the computed value is kept in the atom for further use.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• All code follows the
  Java,
  style guides.
• All code has been tested:
  • Unit tests have been written where possible.

[radeusgd]

Shall we now remove the Lazy.enso from stdlib and replace its usages with ~ fields?
I'd also keep the Lazy_Spec (only remove the eager part, it's worth keeping the rest as the tests nicely serve as additional documentation of this capability) - we can make it still work with:

type Lazy
    Value ~get
    new ~computation = Lazy.Value computation

[JaroslavTulach]

Shall we now remove the Lazy.enso from stdlib and replace its usages with ~ fields?

That's the overall goal. I found just a single usage in SQL_Type_Reference and removed it in 39819fa

I'd also keep the Lazy_Spec

Good idea. Implemented in 160068a

(only remove the eager part,

Eager part works as well.

it's worth keeping the rest as the tests nicely serve as additional documentation of this capability

There was one failing test before cad4e8e was integrated:

enso$ ./built-distribution/enso-engine-0.0.0-dev-linux-amd64/enso-0.0.0-dev/bin/enso --run test/Tests/src/Runtime/Lazy_Spec.enso
Lazy:  [5/6, 162ms]
    - should compute the result only once [21ms]
    - should compute the result only once, even if copied [10ms]
    - should cache the result even if it results in a dataflow error [28ms]
    - [FAILED] should cache the result even if the operation panics [81ms]
        Reason: 2 did not equal 1 (at /home/devel/NetBeansProjects/enso/enso/test/Tests/src/Runtime/Lazy_Spec.enso:72:9-32).
    - should allow to create a Lazy instance that is computed eagerly [8ms]
    - eager mode will not handle dataflow errors/panics specially [11ms]
5 tests succeeded.
1 tests failed.
0 tests skipped.

I'll check what it would take to implement the panic support. Done in cad4e8e

[JaroslavTulach]

bcec688 expands ListBenchmarks with a Lenivý lazy list variant. The lazy list is approximately 10-20% slower - which seems good enough, given the additional check it has to do to remove laziness:

Result "org.enso.interpreter.bench.benchmarks.semantic.ListBenchmarks.mapOverLazyList":
Iteration : 115.037 ms/op

Result "org.enso.interpreter.bench.benchmarks.semantic.ListBenchmarks.mapOverList":
Iteration: 97.133 ms/op

Those 10-20% are only being paid if one requests the laziness. Existing (strict) benchmarks are unaffected by this change. Running benchmarks to verify that - at first sight the results look OK. Let's integrate!

[kustosz]

Nice abuse of the layouting system! Didn't even think this would become possible when I designed it, good to know it extends.

[radeusgd]

This looks great 🎉