This PR adds `Std.Slice.Pattern` instances for `p : Char -> Prop` as
long as `DecidablePred p`, to allow things like `"hello".dropWhile (· =
'h')`.
To achieve this, we refactor `ForwardPattern` and friends to be
"non-uniform", i.e., the class is now `ForwardPattern pat`, not
`ForwardPattern ρ` (where `pat : ρ`).
This PR redefines `String.take` and variants to operate on
`String.Slice`. While previously functions returning a substring of the
input sometimes returned `String` and sometimes returned
`Substring.Raw`, they now uniformly return `String.Slice`.
This is a BREAKING change, because many functions now have a different
return type. So for example, if `s` is a string and `f` is a function
accepting a string, `f (s.drop 1)` will no longer compile because
`s.drop 1` is a `String.Slice`. To fix this, insert a call to `copy` to
restore the old behavior: `f (s.drop 1).copy`.
Of course, in many cases, there will be more efficient options. For
example, don't write `f <| s.drop 1 |>.copy |>.dropEnd 1 |>.copy`, write
`f <| s.drop 1 |>.dropEnd 1 |>.copy` instead. Also, instead of `(s.drop
1).copy = "Hello"`, write `s.drop 1 == "Hello".toSlice` instead.
This PR renames `Substring` to `Substring.Raw`.
This is to signify its status as a second-class citizen (not deprecated,
but no real plans for verification, like `String.Pos.Raw`) and to free
up the name `Substring` for a possible future type `String.Substring :
String -> Type` so that `s.Substring` is the type of substrings of `s`.
The functions `String.toSubstring` and `String.toSubstring'` will remain
for now for bootstrapping reasons.
This PR splits some low-hanging fruit out of `Init.Data.String.Basic`:
basic material about `String.Pos.Raw`, `String.Substrig`, and
`String.Iterator`.
More splitting required and the remaining material is quite unorganized,
but it's a start.
