This PR removes unnecessary parameters from the funcion induction
principles. This is a breaking change; broken code can typically be adjusted
simply by passing fewer parameters.
Part 1, before stage0 update.
Closes#6320
An important part of the interface of a function is the parameter names,
for making used of named arguments. This PR makes the parameter names
print in a reliable way. The parameters of the type now appear as
hygienic names if they cannot be used as named arguments.
Modifies the heuristic for how parameters are chosen to appear before or
after the colon. The rule is now that parameters start appearing after
the colon at the first non-dependent non-instance-implicit parameter
that has a name unusable as a named argument. This is a refinement of
#2846.
Fixes the issue where consecutive hygienic names pretty print without a
space separating them, so we now have `(x✝ y✝ : Nat)` rather than `(x✝y✝
: Nat)`.
Breaking change: `Lean.PrettyPrinter.Formatter.pushToken` now takes an
additional boolean `ident` argument, which should be `true` for
identifiers. Used to insert discretionary space between consecutive
identifiers.
Closes#5810
types like
```
inductive Many (α : Type u) where
| none : Many α
| more : α → (Unit → Many α) → Many α
```
have a `.brecOn` only supports motives producing `Type u`, but not `Sort
u`, but our induction principles produce `Prop`. So the previous
implementation of functional induction would fail for functions that
structurally recurse over such types.
We recognize this case now and, rather hazardously, replace `.brecOn`
with `.binductionOn` (and thus `.below ` with `.ibelow` and `PProd` with
`And`). This assumes that these definitions are highly analogous.
This also improves the error message when realizing a reserved name
fails with an exception, by prepending
```
Failed to realize constant {id}:
```
to the error message.
Fixes#4320
