map_with_index & if then (without else) is broken

[JaroslavTulach]

While working on Dec 3 I realized we have problem with iterating over vectors. The following loops shall behave the same, right? With or without y being present. But they don't!

collect_digits around digits =
    b = Vector.new_builder
    digits.map_with_index y-> row->
        last = row.characters.fold_with_index "" current-> x-> ch->
            case ch of
                '.' ->
                    if current.at 0 == " " then b.append current.trim
                    ""
                digit ->
                    (if around.at y . at x then " "+current else current) + digit
        if last.at 0 == " " then b.append last.trim
    b.to_vector

The program behaves differently with or without following change:

diff --git src/Main.enso src/Main.enso
index b99008b..f60877d 100644
--- src/Main.enso
+++ src/Main.enso
@@ -33,7 +33,6 @@ collect_digits around digits =
                 digit ->
                     (if around.at y . at x then " "+current else current) + digit
         if last.at 0 == " " then b.append last.trim
-        y
     b.to_vector
 
 main =

[JaroslavTulach]

The sample Dec_03.zip project. Unzip and run:

$ enso-engine-0.0.0-dev-linux-amd64/enso-0.0.0-dev/bin/enso --run Dec_03/
540025

Remove y line 36 and execute again:

$ enso-engine-0.0.0-dev-linux-amd64/enso-0.0.0-dev/bin/enso --run Dec_03/
4028

Very disturbing.

[enso-bot]

Pavel Marek reports a new STANDUP for today (2023-12-19):

Progress: - Looking into the bug with map_with_index and if_then.

• Comming up with a smaller reproducer.
• Seems like a problem when if_then's condition is profiled on dataflow error?
• Looking into the problems with TestLogProvider service lookup in project-manager tests - All unit tests use the same testing logging provider #8593 It should be finished by 2023-12-22.

[Akirathan]

This is a smaller reproducer, it is an excerpt from the original Dec_03.zip:

from Standard.Base import all

collect_digits around digits =
    b = Vector.new_builder
    digits.map_with_index y-> row->
        last = row.characters.fold_with_index "" current-> x-> ch->
            case ch of
                '.' ->
                    if current.at 0 == " " then b.append current.trim
                    ""
                digit ->
                    (if around.at y . at x then " "+current else current) + digit
        if last.at 0 == " " then b.append last.trim
        #Nothing
    b.to_vector

main =
    around_small = [[False, False, False, False, False, True, True, True, False, False, False, False, False, False, True, True, True, False, False, False], [False, False, False, False, False, True, True, True, False, False, False, False, False, False, True, True, True, False, False, False]]
    num_small = [".......12.......935.", "............968....."]
    res = collect_digits around_small num_small
    IO.println <| "res.length = " + res.length.to_text

With the commented 14th line (#Nothing), the result is 2, but when uncommenting, the result is 3.

This doesn't look like a bug to me. Then if last.at 0 == "" then b.append last.trim behaves as expected. The thing is that the expression last.at 0 results in an Index_Out_Of_Bounds.Error, and so a dataflow error is returned, instead of Nothing.

[Akirathan]

Closing this as not an issue.

[JaroslavTulach]

last.at 0 results in an Index_Out_Of_Bounds.Error, and so a dataflow error is returned, instead of Nothing

OK, thank you for your investigation, Pavel.