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
Sets the default value to `pp.fieldNotation.generalized` to `true`.
Updates tests, and fixes some minor flaws in the implementation of the
generalized field notation pretty printer.
Now generalized field notation won't be used for any function that has a
`motive` argument. This is intended to prevent recursors from pretty
printing using it as (1) recursors are more like control flow structures
than actual functions and (2) generalized field notation tends to cause
elaboration problems for recursors.
Note: be sure functions that have an `@[app_unexpander]` use
`@[pp_nodot]` if applicable. For example, `List.toArray` needs
`@[pp_nodot]` to ensure the unexpander prints it using `#[...]`
notation.
The `delabConstWithSignature` delaborator is responsible for pretty
printing constants with a declaration-like signature, with binders, a
colon, and a type. This is used by the `#check` command when it is given
just an identifier.
It used to accumulate binders from pi types indiscriminately, but this
led to unfriendly behavior. For example, `#check String.append` would
give
```
String.append (a✝ : String) (a✝¹ : String) : String
```
with inaccessible names. These appear because `String.append` is defined
using patterns, so it never names these parameters.
Now the delaborator stops accumulating binders once it reaches an
inaccessible name, and for example `#check String.append` now gives
```
String.append : String → String → String
```
We do not synthesize names for the sake of enabling binder syntax
because the binder names are part of the API of a function — one can use
`(arg := ...)` syntax to pass arguments by name. The delaborator also
now stops accumulating binders once it reaches a parameter with a name
already seen before — we then rely on the main delaborator to provide
that parameter with a fresh name when pretty printing the pi type.
As a special case, instance parameters with inaccessible names are
included as binders, pretty printing like `[LT α]`, rather than
relegating them (and all the remaining parameters) to after the colon.
It would be more accurate to pretty print this as `[inst✝ : LT α]`, but
we make the simplifying assumption that such instance parameters are
generally used via typeclass inference. Likely `inst✝` would not
directly appear in pretty printer output, and even if it appears in a
hover, users can likely figure out what is going on. (We may consider
making such `inst✝` variables pretty print as `‹LT α›` or
`infer_instance` in the future, to make this more consistent.)
Something we note here is that we do not do anything to make sure
parameters that can be used as named arguments actually appear named
after the colon (nor do we assure that the names are the correct names).
For example, one sees `foo : String → String → String` rather than `foo
: String → (baz : String) → String`. We can investigate this later if it
is wanted.
We also give `delabConstWithSignature` a `universes` flag to enable
turning off pretty printing universe levels parameters.
Closes#2846
