[isabelle] Code-Export: SML value restriction problem?

Hi, I ran into the following problem, where a code generation to SML
produces invalid SML code:

theory Scratch
imports MainÂ
definition "foo â Some (Some o fst)"
export_code foo checking SMLÂ
 (*** ROOT.ML:7: error: Type ('a * 'b -> 'a option) option includes a
free type variable *)

When, however, unfolding the function composition, everything works

definition "bar â Some (Îx. Some (fst x))"
export_code bar checking SML
 (* No error *)

What happened here? Is this a bug in the code generator, or a known

p.s. The generated Scala code is valid in both cases.

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