Here's the latest updated BNF for sweet-expressions' main productions. I
renamed i-expression into it-expression, so that they wouldn't be confused with
SRFI-49. This uses the restart lists' new restart_tail.
I'm omitting the (voluminous) comments, so you can see the main productions at
a glance. There are only 6 productions (rules). As formatted, it's 70 lines
(65 ignoring blank lines). I think it's relatively short and clear.
--- David A. Wheeler
===================================================
restart_tail returns [Object v]:
it_expr rt=restart_tail {$v = cons($it_expr.v, $rt.v);}
| comment_eol retry=restart_tail {$v = $retry.v;}
| restart_end {$v = null;} ;
head returns [Object v]
: PERIOD /* Leading ".": escape following datum like an n-expression. */
(hspace+
(pn=n_expr hspace* {$v = list($pn.v);}
| empty {$v = list(".");} /*= (list '.) */ )
| empty {$v = list(".");} /*= (list '.) */ )
| RESTART hspace* restart_tail hspace*
(rr=rest {$v = cons($restart_tail.v, $rr.v); }
| empty {$v = list($restart_tail.v); } )
| basic=n_expr_first /* Only match n_expr_first */
((hspace+ (br=rest {$v = cons($basic.v, $br.v);}
| empty {$v = list($basic.v);} ))
| empty {$v = list($basic.v);} ) ;
rest returns [Object v]
: PERIOD /* Improper list */
(hspace+
(pn=n_expr hspace* {$v = $pn.v;}
| empty {$v = list(".");})
| empty {$v = list(".");})
| RESTART hspace* restart_tail hspace*
(rr=rest {$v = cons($restart_tail.v, $rr.v);}
| empty {$v = list($restart_tail.v);} )
| scomment hspace* (sr=rest {$v = $sr.v;} | empty {$v = null;} )
| basic=n_expr
((hspace+ (br=rest {$v = cons($basic.v, $br.v);}
| empty {$v = list($basic.v);} ))
| empty {$v = list($basic.v);} ) ;
body returns [Object v] :
it_expr
(same next_body=body {$v = cons($it_expr.v, $next_body.v);}
| dedent {$v = list($it_expr.v);} ) ;
it_expr returns [Object v]
: head
(options {greedy=true;} : (
GROUP_SPLICE hspace* /* Not initial; interpret as splice */
(options {greedy=true;} :
comment_eol error
| empty {$v = monify($head.v);} )
| SUBLIST hspace* sub_i=it_expr /* head SUBLIST it_expr case */
{$v=append($head.v, list(monify($sub_i.v)));}
| comment_eol // Normal case, handle child lines if any:
(indent children=body {$v = append($head.v, $children.v);}
| empty {$v = monify($head.v);} /* No child lines */ )))
| (GROUP_SPLICE | scomment) hspace* /* Initial; Interpet as group */
(group_i=it_expr {$v = $group_i.v;} /* Ignore initial GROUP/scomment */
| comment_eol
(indent g_body=body {$v = $g_body.v;} /* Normal GROUP use */
| same g_i=it_expr {$v = $g_i.v;} /* Plausible separator */
| dedent error ))
| SUBLIST hspace* is_i=it_expr /* "$" as first expression on line */
{$v=list($is_i.v);}
| abbrevh hspace* abbrev_i_expr=it_expr
{$v=list($abbrevh.v, $abbrev_i_expr.v);} ;
t_expr returns [Object v]
: comment_eol t_expr1=t_expr {$v=$t_expr1.v;} /* Initial lcomment, retry */
| (initial_indent_no_bang | hspace+ )
(n_expr {$v = $n_expr.v;} /* indent processing disabled */
| comment_eol t_expr2=t_expr {$v=$t_expr2.v;} )
| initial_indent_with_bang error
| EOF {generate_eof();} /* End of file */
| it_expr {$v = $it_expr.v;} /* Normal case */ ;
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