Fix Value.compare

[filipeom]

No description provided.

[hra687261]

Can you give more details on what the issue with it is?

[filipeom]

Yes of course. In Value.compare the case when two values are not of the same type is undefined and just does: assert false.

smtml/src/ast/value.ml

Lines 46 to 49 in 30dc99f

	| ( ( True | False | Unit | Int _ | Real _ | Str _ | Num _ | List _ | App _
	| Nothing )
	, _ ) ->
	assert false

This isn't a massive issue because we don't have a Expr.compare yet. But even if we had to have an Expr.compare we we could just use the hash-consing tags to provide a total ordering.

But in any case, the function is wrong and we should fix it at some point.