In Isabelle/808e6ddb5a50 there is now a test version of polyml-5.7.1
from the Github repository (there is no release of 5.7.1 yet).
This version works much better for big AFP sessions as 5.7, although
there are slightly more out-of-heap problems than in 5.6.
Here is an example entry for $ISABELLE_HOME/etc/settings:
That is useful for testing, but also for using the ML compiler 5.7,
which provides PIDE markup for scopes of bound variables.
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