[polyml] `Exception- Overflow raised' during functor application

Hi Poly/ML members:

I???m porting MLPolyR from SML/NJ to Poly/ML, and after getting smlnj-lib, ml-yacc and ml-lex loaded with Poly/ML I try to load the parser but the following error occurs:

``` Exception- Overflow raised Exception- Overflow raised ```

and `poly` quits.

Here's a minimal setup that can reproduce the issue:

https://github.com/owo-lang/MLPolyR/tree/polyml_debug

Clone the tree and checkout `polyml_debug` branch,

``` poly --use load.sml ```

It already contains smlnj-lib, ml-yacc and ml-lex from MLton 20180207 releases.

My platform is macOS Mojave 10.14.4, Poly/ML version is 5.8 Release.

With the same setup MLton can compile the source without such an issue. (via `mlton mlpolyr.mlb`)

Hints on what could be the cause?

Thank you for any help you can offer.

LdBeth.