Once again I have entangled two conceptually distinct changes into a
single commit because demuxing them from the diff is too much work.
Alas. Let's break it down.
The simpler part of this change is to reintroduce "space strings" with
a slightly fresh coat of paint. We now have 3 different types of
string leaders that can be used together. So we now have:
| directly concatenates this line with the previous line
> prepends an LF character before concatenation
+ (NEW) prepends a single space character before concatenation
The `+` leader enables more æsthetic soft line wrapping than `|`
because it doesn't require the use of leading or trailing the
whitespace to separate words, as long as lines are broken at word
boundaries. Perhaps this is not as common a usecase as I am making it,
but I do like to hard wrap paragraphs in documents, so if anything,
it's a feature for me.
As I was considering what character to use for this leader, I realized
that I wanted to be able to support numeric map keys, a la:
-1: negative one
0: zero
+1: positive one
But previously this would not parse correctly, as the tokenizer would
find `-` and expect it to be followed by a space to indicate a list
item (and the additional string leader would cause the same problem
with `+`). I wanted to support this use case, so the parser was
changed to take a second pass on lines starting with the string
leaders (`|`, `+`, and `>`) and the list item leader (`-`) if the
leader has a non-space character following it. Note that this does not
apply to the comment leader (`#` not followed by a space or a newline
is a tokenization error) or to the inline list/map leaders(since those
do not respect internal whitespace, there is no way to treat them
unambiguously).
To reduce the likelihood of confusing documents, scalars are no longer
allowed to occupy their own line (the exception to this is if the
document consists only of a scalar value). Inline lists and maps can
still occupy their own line, though I am considering changing this as
well to force them to truly be inline. I think this change makes
sense, as scalars are generally intended to be represent an unbroken
single item serialization of some non-string value. In other words,
# these two lines used to parse the same way
key: 9001
# but now the following line is a parse error due to the scalar
# occupying its own line
key:
9001
# also, this still works, but it may be changed to be an error in
# the future
key:
[ 9, 0, 0, 1 ]
Inline maps have also been changed so that their keys can start with the
now-unforbidden string leaders and list item leader characters.
The way I implemented these changes ended up being directly coupled and
I am not interested in trying to decouple them, so instead here's a
single commit that makes changes to both the API and the format. Let's
go over these.
| now acts as a direct concatenation operator, rather than
concatenating with a space. This is because the format allows the
specification of a trailing space (by using | to fence the string just
before the newline). So it's now possible to spread a long string
without spaces over multiple lines, which couldn't be done before.
This does have the downside that the common pattern of concatenating
strings with a space now requires some extra trailing line noise. I
may introduce a THIRD type of concatenating string (thinking of
using + as the prefix) because I am a jerk. We will see.
The way multi-line strings are concatenated has changed. Partially this
has to do with increasing the simplicity of the aforementioned
implementation change (the parser forgets the string type from the
tokenizer. This worked before because there would always be a trailing
character that could be popped off. But since one type now appends no
character, this would have to be tracked through the parsing to
determine if a character would need to be popped at the end). But I
was also not terribly satisfied with the semantics of multiline
strings before. I wrote several words about this in
429734e6e813b225654aa71c283f4a8b4444609f, where I reached the opposite
conclusion from what is implemented in this commit.
Basically, when different types of string concatenation are mixed, the
results may be surprising. The previous approach would append the line
terminator at the end of the line specified. The new approach prepends
the line terminator at the beginning of the line specified. Since the
specifier character is at the beginning of the line, I feel like this
reads a little better simply due to the colocation of information. As
an example:
> first
| second
> third
Would previously have resulted in "first\nsecondthird" but it will now
result in "firstsecond\nthird". The only mildly baffling part about
this is that the string signifier on the first line has absolutely no
impact on the string. In the old design, it was the last line that had
no impact.
Finally, this commit also changes Value so that it uses []const u8
slices directly to store strings instead of ArrayLists. This is
because everything downstream of the value was just reaching into
string.items to access the slice directly, so cut out the middleman.
It was unintuitive to access a field named .string and get an
arraylist rather than a slice, anyway.
This commit makes both the parser and tokenizer a lot more willing to
accept whitespace in places where it would previously cause strange
behavior. Also, whitespace is ignored preceding and following all
values and keys in flow-style objects now (in regular objects,
trailing whitespace is an error, and it is also an error for non-flow
map keys to have whitespace before the colon). Tabs are no longer
allowed as whitespace in the line. They can be inside scalar values,
though, including map keys. Also strings allow tabs inside of them.
The primary motivation here is to apply the principle of least
astonishment. For example, the following
- [hello, there]
would previously have been parsed as the scalar " [hello, there]" due
to the presence of an additional space after the "-" list item
indicator. This obviously looks like a flow list, and the way it was
previously parsed was very visually confusing (this change does mean
that scalars cannot start with [, but strings can, so this is not a
real limitation. Note that strings still allow leading whitespace, so
> hello
will produce the string " hello" due to the additional space after the
string designator. For flow lists,
[ a, b ]
would have been parsed as ["a", "b "], which was obviously confusing.
The previous commit fixed this by making whitespace rules more strict.
This commit fixes this by making whitespace rules more relaxed. In
particular, all whitespace preceding and following flow items is now
stripped. The main motivation for going in this direction is to allow
aligning list items over multiple lines, visually, which can make data
much easier to read for people, an explicit design goal. For example
key: [ 1, 2, 3 ]
other: [ 10, 20, 30 ]
is now allowed. The indentation rules do not allow right-aligning
"key" to "other", but I think that is acceptable (if we forced using
tabs for indentation, we could actually allow this, which I think is
worth consideration, at least). Flow maps are more generous:
foo: { bar: baz }
fooq: { barq: bazq }
is allowed because flow maps do not use whitespace as a structural
designator. These changes do affect how some things can be
represented. Scalar values can no longer contain leading or trailing
whitespace (previously the could contain leading whitespace). Map keys
cannot contain trailing whitespace (they could before. This also means
that keys consisting of whitespace cannot be represented at all).
Ultimately, given the other restrictions the format imposes on keys
and values, I find these to be acceptable and consistent with the goal
of the format.
The errors in the line buffer and tokenizer now have diagnostics. The
line number is trivial to keep track of due to the line buffer, but
the column index requires quite a bit of juggling, as we pass
successively trimmed down buffers to the internals of the parser.
There will probably be some column index counting problems in the
future. Also, handling the diagnostics is a bit awkward, since it's a
mandatory out-parameter of the parse functions now. The user must
provide a valid diagnostics object that survives for the life of the
parser.
Since the tokenizer is decoupled from the parser, there's no good way
to do this. Also without attempting to parse the last line, it's
impossible to say if it is junk data or simply a missing trailing new
line.
When the buffer was separated from the tokenizer, we lost some
validation, including really aggressive carriage return detection.
This brings this back in full force and adds some additional
validation on top of it.
I don't like big monolithic source files, so let's restructure a bit.
parser.zig is still bigger than I would like it to be, but there isn't
a good way to break up the two state machine parsers, which take up
most of the space. This is the last junk commit before I am seriously
going to implement the "streaming" parser. Which is the last change
before implementing deserialization to object. I am definitely not
just spinning my wheels here.
