Below is an extracted ANTLR description of sweet-expressions. "n_expr_first"
is an n-expression that doesn't match an abbreviation followed by a horizontal
space (hspace, aka space or tab). See the "devel" branch for the whole thing.
Thoughts? Comments? It's like to have some errors, and certainly has some
omissions.
I'm not sure how to handle #|...|# at top level when nothing else on line - it
needs to be skipped and completely ignored. Suggestions welcome.
--- David A. Wheeler
=======================================================
abbrevh : APOSH | QUASIQUOTEH | UNQUOTE_SPLICEH |
UNQUOTEH;
abbrev_noh : APOS | QUASIQUOTE | UNQUOTE_SPLICE | UNQUOTE ;
abbrev_all : abbrevh | abbrev_noh;
splice : GROUP; // Use this synonym to make its purpose clearer.
sublist : DOLLAR; // Use this synonym to make its purpose clearer.
// Whitespace & indentation names
ichar : SPACE | TAB | BANG ; // indent char
hspace : SPACE | TAB ; // horizontal space
wspace : hspace; // or eolchars
// Read in ;comment (if exists), followed by EOL. On a non-tokeninzing parser,
// this may reset indent as part of EOL processing.
eol_comment_lines : LCOMMENT? EOL;
// The "head" is the production for 1+ n-expressions on one line; it will
// return the list of n-expressions on the line.
head : n_expr_first hspace* rest;
// The "rest" production reads the rest of the expressions on a line ("rest of
the head"),
// after the first expression of the line.
rest : PERIOD hspace+ n_expr hspace* /* improper list. Error if n_expr at
this point */
| BLOCK_COMMENT hspace* rest
| DATUM_COMMENT_START hspace* n_expr hspace* rest // Ignore the next
datum
| n_expr hspace* rest
| /* empty: ; eol */;
// body handles the sequence of 1+ child lines in an i_expr.
body : i_expr (SAME body | DEDENT);
i_expr : head ( splice hspace* (i_expr | eol_comment_lines (INDENT body)?)
| DOLLAR hspace* (i_expr | eol_comment_lines (INDENT body)?)
| eol_comment_lines (INDENT body)?
) // child lines
| (GROUP | BLOCK_COMMENT) hspace* (i_expr | eol_comment_lines INDENT
body)
| DOLLAR hspace* (i_expr | eol_comment_lines INDENT body)
| abbrevh hspace* i_expr;
t_expr : i_expr
| eol_comment_lines t_expr
| hspace+ (n_expr /* indent processing disabled */
| eol_comment_lines t_expr /* try again */
| BANG /* error */)
| BANG /* error */
| EOF;
------------------------------------------------------------------------------
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