This allows for retyping after monomorphisation: a new function just extracts
the return type of the operator, without checking the operand types.
Also to avoid multiplying function arguments around the typer, the flags have
been gathered in a record that is included in the typing environment; it's ok to
give them default values as long as these are the strictest.
so don't retype after monomorphisation, which is now possible as the pass itself
correctly preserves types.
In time the typer will need a special case to get knowledge of the new types and
modified operator types.
A little bit of effort enables us to propagate valid typing annotations, making
subsequent typing re-inference easier (and avoiding a traversal just to remove
type annotations)
since it doesn't correctly propagate and update types. (Ideally it would, but
otherwise it would be better to remove the type annotations on the fly instead
of introducing wrong ones then cleaning them up).
The primary use-case for this was to be able to run computations on a list of
structures, then return an updated list with some fields in the structures
modified : that is what we need for distribution of tax amounts among household
members, for example.
This patch has a few components:
- Addition of a test as an example for tax distributions
- Added a transformation, performed during desugaring, that -- where lists are
syntactically expected, i.e. after the `among` keyword -- turns a (syntactic)
tuple of lists into a list of tuples ("zipping" the lists)
- Arg-extremum transformation was also fixed to use an intermediate list instead
of computing the predicate twice
- For convenience, allow to bind multiple variables in most* list
operations (previously only `let in` and functions allowed it)
- Fixed the printer for tuples to differentiate them from lists
*Note: tuples are not yet allowed on the left-hand side of filters and
arg-extremums for annoying syntax conflict reasons.
