More grammar shite.

6 files changed, 354 insertions, 9 deletions

diff --git a/docs/c1/1-parse.md b/docs/c1/1-parse.md
index a23ebbc..e04240b 100644
--- a/docs/c1/1-parse.md
+++ b/docs/c1/1-parse.md
@@ -1,8 +1,7 @@
 # Parser for Code & Data
 
-Zisp s-expressions are defined in terms of an extremely minimal set of data
-types; only that which is necessary to build representations of more complex
-expressions and data types:
+Zisp S-Expressions represent an extremely minimal set of data types; only that
+which is necessary to strategically construct more complex code and data:
 
     +--------+-----------------+--------+----------+------+
     | TYPE   | String          | Rune   | Pair     | Nil  |
@@ -10,12 +9,8 @@ expressions and data types:
     | E.G.   | foo, |foo bar|  | #name  | (X & Y)  | ()   |
     +--------+-----------------+--------+----------+------+
 
-Note that the ampersand replaces the period in pair notation.  This simplifies
-the grammar: periods are a regular constituent of strings, while the ampersand
-cannot appear in unquoted strings.
-
 The parser can also output non-negative integers, but this is only used for
-datum labels; number literals are handled by the *decoder*.
+datum labels; number literals are handled by the *decoder* (see next).
 
 The parser recognizes various "syntax sugar" and transforms it into uses of the
 above data types.  The most ubiquitous example is of course the list:
@@ -110,6 +105,8 @@ Further notes about the syntax sugar table and examples above:
   Zisp's internal use and standard library; users can use lowercase runes with
   custom meaning without worrying about clashes.
 
+For an exact specification of the grammar, see [grammar](grammar.html).
+
 <!--
 ;; Local Variables:
 ;; fill-column: 80
diff --git a/docs/c1/2-decode.md b/docs/c1/2-decode.md
index 0b34204..379c74b 100644
--- a/docs/c1/2-decode.md
+++ b/docs/c1/2-decode.md
@@ -1,7 +1,7 @@
 # Decoding
 
 A separate process called "decoding" can transform simple data structures,
-consisting of only the datum types, into a richer set of Zisp types.
+consisting of only the base datum types, into a richer set of Zisp types.
 
 For example, the decoder may turn `(#HASH ...)` into a vector, as one would
 expect a vector literal like `#(...)` to work in Scheme.  Bytevector syntax
diff --git a/docs/c1/grammar.abnf.txt b/docs/c1/grammar.abnf.txt
new file mode 100644
index 0000000..ad68a16
--- /dev/null
+++ b/docs/c1/grammar.abnf.txt
@@ -0,0 +1,109 @@
+; Compatible with https://www.quut.com/abnfgen/
+
+; It's unclear whether this grammar is truly complete.  It has been
+; verified not to produce text that is rejected by the Zisp parser
+; --except for Unicode escape sequences for surrogate code points--
+; but there may be some text that is accepted by the parser despite
+; not being grammatical according to these rules.
+
+
+Stream        = [ Unit *( Blank Unit ) ] *Blank [Trail]
+
+
+Unit          = *Blank Datum
+
+Blank         = HTAB / LF / %x0b / %x0c / CR / SP / Comment
+
+Trail         = SkipLine / SkipUnit / ';' '~' *Blank
+
+
+Datum         = BareString / DottedStr / CladDatum / Rune / RuneStr
+              / RuneDotStr / RuneClad / LabelRef / LabelDef / HashStr
+              / HashDotStr / HashClad / QuoteExpr / JoinExpr
+
+Comment       = SkipLine LF / SkipUnit Blank
+
+SkipLine      = ';' [ SkipLStart *AnyButLF ]
+
+SkipUnit      = ';' '~' Unit
+
+SkipLStart    = %x00-09 / %x0b-7d / %x7f-ff ; any but LF or '~'
+
+AnyButLF      = %x00-09 / %x0b-ff
+
+
+BareString    = BareChar *( BareChar / Numeric )
+
+DottedStr     = ( '.' / Numeric ) *( '.' / Numeric / BareChar )
+
+CladDatum     = '|' *( PipeStrChar / '\' StringEsc ) '|'
+              / '"' *( QuotStrChar / '\' StringEsc ) '"'
+              / '(' List ')'
+              / '[' List ']'
+              / '{' List '}'
+
+Rune          = '#' RuneName
+
+RuneStr       = '#' RuneName '\' BareString
+
+RuneDotStr    = '#' RuneName '\' DottedStr
+
+RuneClad      = '#' RuneName CladDatum
+
+LabelRef      = '#' '%' Label '%'
+
+LabelDef      = '#' '%' Label '=' Datum
+
+HashStr       = '#' '\' BareString
+
+HashDotStr    = '#' '\' DottedStr
+
+HashClad      = '#' CladDatum
+
+QuoteExpr     = "'" Datum
+              / '`' Datum
+              / ',' Datum
+
+JoinExpr      = Datum RJoinDatum
+              / LJoinDatum NoStartDot
+              / Datum ':' Datum
+              / NoEndDot '.' Datum
+
+
+BareChar      = '!' / '$' / '%' / '*' / '/' / '<' / '=' / '>'
+              / '?' / '@' / '^' / '_' / '~' / ALPHA
+
+Numeric       = '+' / '-' / DIGIT
+
+PipeStrChar   = %x00-5b / %x5d-7b / %x7d-ff ; any but '|' or '\'
+
+QuotStrChar   = %x00-21 / %x23-5b / %x5d-ff ; any but '"' or '\'
+
+StringEsc     = '\' / '|' / '"' / *( HTAB / SP ) LF *( HTAB / SP )
+              / 'a' / 'b' / 't' / 'n' / 'v' / 'f' / 'r' / 'e'
+              / 'x' 1*( 2HEXDIG ) ';'
+              / 'u' ['0'] 1*5HEXDIG ';'
+              / 'u' '1' '0' 4HEXDIG ';'
+
+List          = [ Unit *( Blank Unit ) ] *Blank [Tail] [SkipUnit]
+
+Tail          = '&' Unit *Blank
+
+
+RuneName      = ALPHA *5( ALPHA / DIGIT )
+
+Label         = 1*12( HEXDIG )
+
+
+RJoinDatum    = CladDatum / Rune / RuneStr / RuneDotStr / RuneClad
+              / LabelRef / LabelDef / HashStr / HashDotStr / HashClad
+              / QuoteExpr
+
+LJoinDatum    = CladDatum / RuneClad / LabelRef / HashClad
+
+NoStartDot    = BareString / CladDatum / Rune / RuneStr / RuneDotStr
+              / RuneClad / LabelRef / LabelDef / HashStr / HashDotStr
+              / HashClad / QuoteExpr
+
+NoEndDot      = BareString / Rune / RuneStr / RuneClad / LabelRef
+              / HashStr / HashClad
diff --git a/docs/c1/grammar.md b/docs/c1/grammar.md
new file mode 100644
index 0000000..3364150
--- /dev/null
+++ b/docs/c1/grammar.md
@@ -0,0 +1,101 @@
+# Zisp S-Expression Grammar
+
+The grammar is available in several different formats:
+
+* [ZBNF](grammar.zbnf.txt): See below for the rules of this notation
+* [ABNF](grammar.abnf.txt): Compatible with the `abnfgen` tool
+* [PEG](grammar.peg.txt): Compatible with `peg/leg` tool
+
+
+## ZBNF notation
+
+The ZBNF grammar specification uses a BNF-like notation with PEG-like
+semantics:
+
+* Concatenation of expressions is implicit: `foo bar` means `foo`
+  followed by `bar`.
+
+* Parentheses are used for grouping, and the pipe symbol `|` is used
+  for alternatives.
+
+* The suffixes `?`, `*`, and `+` have the same meaning as in regular
+  expressions, although `[foo]` is used in place of `(foo)?`.
+
+* The syntax is defined in terms of bytes, not characters.  Terminals
+  `'c'` and `"c"` refer to the ASCII value of the given character `c`.
+  Standard C escape sequences are supported.
+
+* The prefix `~` means NOT.  It only applies to rules that match one
+  byte, and negates them.  For example, `~( 'a' | 'b' )` matches any
+  byte other than 'a' and 'b'.
+
+* Ranges of terminal values are expressed as `x...y` (inclusive).
+
+* ABNF "core rules" like `ALPHA` and `HEXDIG` are supported.
+
+* There is no ambiguity, or look-ahead / backtracking beyond one byte.
+  Rules match left to right, depth-first, and greedy.  As soon as the
+  input matches the first terminal of a rule --explicit or implied by
+  recursively descending into the first non-terminal-- it must match
+  that rule to the end or a syntax error is reported.
+
+The last point makes the notation simple to translate to code.
+
+
+## Limitations outside the grammar
+
+The following limits are not represented in the grammar:
+
+* A `UnicodeSV` is the hexadecimal representation of a Unicode scalar
+  value; it must represent a value in the range 0 to D7FF, or E000 to
+  10FFFF, inclusive.  Any other value signals an error.  Valid values
+  are converted into a UTF-8 byte sequence encoding the value.
+
+* A `Rune` longer than 6 bytes is grammatical, but signals an error.
+  This is important because runes are not self-terminating; defining
+  their grammar as ending after a maximum of 6 bytes would allow
+  another datum beginning with an alphabetic character to follow a
+  rune immediately without any visual delineation, which would be
+  terribly confusing for a human reader.  Consider: `#foobarbaz`.
+  This would parse as a `Datum` joining `#foobar` and `baz`.
+
+* A `Label` is the hexadecimal representation of a 48-bit integer,
+  meaning it allows for a maximum of 12 hexadecimal digits.  Longer
+  values are grammatical, but signal an out-of-range error, so as to
+  avoid signaling a confusing "invalid character" error on input that
+  appears grammatical.  Consider: `#%123456789abcd=foo`.  This would
+  signal an invalid character error at the letter `d` if the grammar
+  limited a `Label` to 12 hexadecimal digits.
+
+
+## Stream-parsing strategy
+
+The parser consumes one `Unit` from the input stream every time it's
+called; it returns the `Datum` therein if found, or else it returns
+the Zisp EOF token.
+
+Since a `Datum` is not self-terminating, the parser must read beyond
+it to realize that it has ended (if not followed by the EOF).  Thus,
+it will consume one more `Blank` following the `Unit` that it parsed.
+If this `Blank` is a comment, it will be consumed entirely, ensuring
+that parsing resumes properly on a subsequent parser call on the same
+input stream, without needing to store any state in between.
+
+Since comments of type `SkipUnit` are likewise not self-terminating,
+an arbitrary number of chained `SkipUnit` comments may need to be
+consumed before the parser is finally allowed to return.
+
+The following illustration shows the positions at which the parser
+will stop consuming input when called repeatedly on the same input
+stream.  The dots represent the extent of each `Unit` being parsed,
+while the caret points at the last byte the parser will consume in
+that parse cycle.
+
+```
+foo (bar)[baz] foo;~bar foo;~bar;~baz;~bat foobar
+...^..........^...     ^...               ^......^
+```
+
+Notice how, in the fourth cycle, the parser is forced to consume all
+commented-out units before it can return, since it would otherwise
+leave the stream in an inappropriate state.
diff --git a/docs/c1/grammar.peg.txt b/docs/c1/grammar.peg.txt
new file mode 100644
index 0000000..d194652
--- /dev/null
+++ b/docs/c1/grammar.peg.txt
@@ -0,0 +1,75 @@
+# Compatible with https://piumarta.com/software/peg
+
+Stream       <- Unit ( Blank Unit )* !.
+
+Unit         <- Blank* Datum
+
+
+Blank        <- [\t-\r ] / Comment
+
+Datum        <- OneDatum ( JoinChar? OneDatum )*
+
+JoinChar     <- '.' / ':'
+
+
+Comment      <- ';' ( SkipUnit / SkipLine )
+
+SkipUnit     <- '~' Unit
+
+SkipLine     <- (!'\n' .)* '\n'?
+
+
+OneDatum     <- BareString / CladDatum
+
+
+BareString   <- ( '.' / '+' / '-' / DIGIT ) ( BareChar / '.' )*
+              / BareChar+
+
+CladDatum    <- PipeStr / QuoteStr / HashExpr / QuoteExpr / List
+
+PipeStr      <- '|' ( PipeStrChar / '\' StringEsc )* '|'
+QuoteStr     <- '"' ( QuotStrChar / '\' StringEsc )* '"'
+HashExpr     <- '#' ( RuneExpr / LabelExpr / HashDatum )
+QuoteExpr    <- "'" Datum / '`' Datum / ',' Datum
+List         <- ParenList / SquareList / BraceList
+
+BareChar     <- ALPHA / DIGIT
+              / '!' / '$' / '%' / '*' / '+'
+              / '-' / '/' / '<' / '=' / '>'
+              / '?' / '@' / '^' / '_' / '~'
+
+PipeStrChar  <- (![|\\] .)
+QuotStrChar  <- (!["\\] .)
+
+StringEsc    <- '\' / '|' / '"' / ( HTAB / SP )* LF ( HTAB / SP )*
+              / 'a' / 'b' / 't' / 'n' / 'v' / 'f' / 'r' / 'e'
+              / 'x' HexByte+ ';'
+              / 'u' UnicodeSV ';'
+
+HexByte      <- HEXDIG HEXDIG
+UnicodeSV    <- HEXDIG+
+
+RuneExpr     <- Rune ( '\' BareString / CladDatum )?
+LabelExpr    <- '%' Label ( '%' / '=' Datum )
+HashDatum    <- '\' BareString / CladDatum
+
+Rune         <- ALPHA ( ALPHA / DIGIT )*
+Label        <- HEXDIG+
+
+ParenList    <- '(' ListBody ')'
+SquareList   <- '[' ListBody ']'
+BraceList    <- '{' ListBody '}'
+
+ListBody     <- Unit* ( Blank* '&' Unit )? Blank*
+
+DIGIT        <- [0-9]
+ALPHA        <- [a-zA-Z]
+HEXDIG       <- [0-9a-fA-F]
+
+
+# This file should be kept in perfect sync with zbnf.txt for easy
+# comparison between the two.
+
+# Due to a quirk in the peg tool this file is used with, the grammar
+# must not allow an empty stream.  Therefore, the Unit rule has its
+# Datum declared as mandatory rather than optional.
diff --git a/docs/c1/grammar.zbnf.txt b/docs/c1/grammar.zbnf.txt
new file mode 100644
index 0000000..a8792f0
--- /dev/null
+++ b/docs/c1/grammar.zbnf.txt
@@ -0,0 +1,63 @@
+# Custom notation with PEG semantics; see grammar.html
+
+Stream        : Unit ( Blank Unit )*
+
+Unit          : Blank* [Datum]
+
+
+Blank         : '\t'...'\r' | SP | Comment
+
+Datum         : OneDatum ( [JoinChar] OneDatum )*
+
+JoinChar      : '.' | ':'
+
+
+Comment       : ';' ( SkipUnit | SkipLine )
+
+SkipUnit      : '~' Unit
+
+SkipLine      : ( ~LF )* [LF]
+
+
+OneDatum      : BareString | CladDatum
+
+
+BareString    : ( '.' | '+' | '-' | DIGIT ) ( BareChar | '.' )*
+              | BareChar+
+
+CladDatum     : PipeStr | QuoteStr | HashExpr | QuoteExpr | List
+
+PipeStr       : '|' ( PipeStrChar | '\' StringEsc )* '|'
+QuoteStr      : '"' ( QuotStrChar | '\' StringEsc )* '"'
+HashExpr      : '#' ( RuneExpr | LabelExpr | HashDatum )
+QuoteExpr     : "'" Datum | '`' Datum | ',' Datum
+List          : ParenList | SquareList | BraceList
+
+BareChar      : ALPHA | DIGIT
+              | '!' | '$' | '%' | '*' | '+'
+              | '-' | '/' | '<' | '=' | '>'
+              | '?' | '@' | '^' | '_' | '~'
+
+PipeStrChar   : ~( '|' | '\' )
+QuotStrChar   : ~( '"' | '\' )
+
+StringEsc     : '\' | '|' | '"' | ( HTAB | SP )* LF ( HTAB | SP )*
+              | 'a' | 'b' | 't' | 'n' | 'v' | 'f' | 'r' | 'e'
+              | 'x' HexByte+ ';'
+              | 'u' UnicodeSV ';'
+
+HexByte       : HEXDIG HEXDIG
+UnicodeSV     : HEXDIG+
+
+RuneExpr      : Rune [ '\' BareString | CladDatum ]
+LabelExpr     : '%' Label ( '%' | '=' Datum )
+HashDatum     : '\' BareString | CladDatum
+
+Rune          : ALPHA ( ALPHA | DIGIT )*
+Label         : HEXDIG+
+
+ParenList     : '(' ListBody ')'
+SquareList    : '[' ListBody ']'
+BraceList     : '{' ListBody '}'
+
+ListBody      : Unit* [ Blank* '&' Unit ] Blank*