Playground: Recursive tree with polymorphic variants blows up the stack

[fhammerschmidt]

The following example yields a stack overflow error on the playground

https://rescript-lang.org/try?version=v11.0.0-beta.4&code=DYUwLgBATiDGEGcCuBbCBeCAPDA+AUBIgO4CWYsAFthAN6EQA+EAxADIgCGAZnhAAwNmLAHIB7ACYgAFADdOwJCAA0EUNzCqopAOaUwASj7zFICAGo1IDQFpcyNJe16wdhwwC++fKEgoAngAqMGaYopIyDACMygzhUtIATKrxMgAsKRw8mVzcBiniCQBsOdmsWXn5cYUyAMwFEdIArKXcrfmsNdIA7K3tVQbevhDSRpgBwSAgbqh2AFIIAHTAYjr4QA

The same with normal variants does not

https://rescript-lang.org/try?version=v11.0.0-beta.4&code=C4TwDgpgBAThDGVhwgHgOQDcCGAbArhAHxQC8AUFFAD5QAyE2AZpTVAHID2AJhABRY8hADRIUGHAWKjkENIKlEAlOXK4IwWAigBnfAFsyUAB5kirHQHcAlsHgALE1ADerWg2ZmoABjcce-JIiUOpMwKIw1gDm9sBKXkHQANQhEGEAtER6himRMcCZ2awAvqrqmvogACooRly8fKwAjMKs9fwATKLtfAAsoh5MA4xMSt0BfABsw8wzo2NtEwDM4w0ArHNzY-4NAOyb9CNKCypqGlB88aRQlTVyhQaZAFI6AHS4nFHkQA

Melange Playground can do the polymorphic one without problems:

https://melange.re/unstable/playground/?language=Reason&code=bGV0IHJlYyBzdW0gPSBmdW4KICB8IGBMZWFmID0%2BIDAKICB8IGBOb2RlKHZhbHVlLCBsZWZ0LCByaWdodCkgPT4gdmFsdWUgKyBsZWZ0LT5zdW0gKyByaWdodC0%2Bc3VtCgpsZXQgbXlUcmVlID0gYE5vZGUoCiAgMSwKICBgTm9kZSgyLCBgTm9kZSg0LCBgTGVhZiwgYExlYWYpLCBgTm9kZSg2LCBgTGVhZiwgYExlYWYpKSwKICBgTm9kZSgzLCBgTm9kZSg1LCBgTGVhZiwgYExlYWYpLCBgTm9kZSg3LCBgTGVhZiwgYExlYWYpKSwKKQoKbGV0ICgpID0gbXlUcmVlLT5zdW0tPkpzLmxvZwo%3D&live=off

I also tested the polyvariants example locally with ReScript 11, where it compiles fine.

[fhammerschmidt]

Ok, so the polymorphic one also compiles when it's typed out and annotated!

https://rescript-lang.org/try?version=v11.0.0-beta.4&code=C4TwDgpgBAThDGVhwgHgOQDcCGAbArhAHxQC8UA2gFBRQA+UAxADITYBmN9TAcgPYATCAAoseQgBokKDDgLEpyCGjHyiASioBdKlVwRgsBFADO+ALZkowgB4Auactnji6skS4mA7gEtg8AAsoGygAby4GFjZ2dygABgjeQRE5SSh9dmApGB8AcwDgN1ISVOgAanSITIBaIjNLCpz84Fr6rgBfXX1DcxAAFRQrRn4hYS4ARgkuYeThACYpGdGAFkXWDjXo9UWRkQA2TY2mdfZ1bend4QBmHdmAVkP2R+2k0YB2R+fzzT0DayKoL0BspWhZagApEwAOlwfFyVCAA

[fhammerschmidt]

To summarize the issue:

• This yields a stack overflow

  let rec sum = x =>
    switch x {
    | #Leaf => 0
    | #Node(value, left, right) => value + left->sum + right->sum
    }
  
  let myTree = #Node(
    1,
    #Node(2, #Node(4, #Leaf, #Leaf), #Node(6, #Leaf, #Leaf)),
    #Node(3, #Node(5, #Leaf, #Leaf), #Node(7, #Leaf, #Leaf)),
  )
  
  let () = myTree->sum->Js.log

• This one compiles

  type rec tree<'value> = [
    | #Leaf
    | #Node('value, tree<'value>, tree<'value>)
  ]
  
  let rec sum = (x: tree<'value>) =>
    switch x {
    | #Leaf => 0
    | #Node(value, left, right) => value + left->sum + right->sum
    }
  
  let myTree = #Node(
    1,
    #Node(2, #Node(4, #Leaf, #Leaf), #Node(6, #Leaf, #Leaf)),
    #Node(3, #Node(5, #Leaf, #Leaf), #Node(7, #Leaf, #Leaf)),
  )
  
  let () = myTree->sum->Js.log

[fhammerschmidt]

Fixed now.