@Kha It seems the recent parser modifications created some unexpected
problems. I didn't investigate them. I am "lost" in the elaborator and
dependent pattern matching land.
1) We can't write anymore
```
f [1, 2, 3] |>.run' 0 = Except.ok ()
```
We have to use parentheses and the error message is weird :(
```
(f [1, 2, 3] |>.run' 0) = Except.ok ()
```
2) I had to add comments to `macro.lean`, I didn't find a workaround
for one of the rules. BTW, I had to add a bunch of `:term` for fixing
the other rules, and the error messages were counterintuitive.
It is an undefined behavior in C when the right operand of a shift operation exceeds the bit-width of the left operand.
We define the shift operation to be `x << (y % B)` where `B` is the bit-width of the left operand.
@Kha this is a fix for the example that @gebner posted on Zulip.
There are other possible workarounds, but I think this one is
"intuitive".
Here is the problem description and workaround.
We currently use the `withPosition` combinator at `matchAlts`. The
original motivation was nested `match`-expressions without
parenthesis.
We also have the `checkColGt` in the application parser.
Thus, `frob 5` is not parsed as an application. That is, the term
parser after the `then` keyword stops at `frob`.
Then, we get the weird "expected 'else'" error message at `5` :)
In this commit, I add a `checkColGe` check at the beginning of each
alternative right-hand-side.
The effect on the stdlib was minimal. It basically affected old code
that used the Lean 3 workaround for partial functions
```
partial def f : N -> N | i =>
...
```
In Lean 4, we can use the more natural
```
partial def f (i : N) : N :=
...
```
or
```
partial def f : N -> N := fun i =>
...
```
It also affected code such as
```
instance : Repr String.Iterator where
reprPrec | ⟨s, pos⟩, prec =>
Repr.addAppParen ("String.Iterator.mk " ++ reprArg s ++ " " ++ reprArg pos) prec
```
This is a workaround for a missing feature. We really wanted to write
```
instance : Repr String.Iterator where
reprPrec ⟨s, pos⟩ prec :=
Repr.addAppParen ("String.Iterator.mk " ++ reprArg s ++ " " ++ reprArg pos) prec
```
