Here are the key BNF definitions. These change FF/VT processing based on John
Cowan's recent comment.
Now uncommented FF/VT have to be on their own line, and they terminate any
current t-expression.
Again: Are we done? Any improvements or recommended changes?
--- David A. Wheeler
=== Sweet-expression BNF ====
restart_tail returns [Object v]
: it_expr more=restart_tail {$v = cons($it_expr.v, $more.v);}
| comment_eol retry1=restart_tail {$v = $retry1.v;}
| (FF | VT)+ EOL retry2=restart_tail {$v = $retry2.v;}
| restart_end {$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 = $g_i.v;} /* Plausible separator */
/* Handle #!sweet EOL EOL t_expr */
| comment_eol restart=t_expr {$v = $restart.v;} )
| dedent error ))
| SUBLIST hspace* is_i=it_expr {$v=list($is_i.v);} /* "$" first on line */
| abbrevh hspace* abbrev_i_expr=it_expr
{$v=list($abbrevh.v, $abbrev_i_expr.v);} ;
t_expr returns [Object v]
: comment_eol retry1=t_expr {$v=$retry1.v;}
| (FF | VT)+ EOL retry2=t_expr {$v=$retry2.v;}
| (initial_indent_no_bang | hspace+ )
(n_expr {$v = $n_expr.v;} /* indent processing disabled */
| comment_eol retry3=t_expr {$v=$retry3.v;} )
| initial_indent_with_bang error
| EOF {generate_eof();} /* End of file */
| it_expr {$v = $it_expr.v;} /* Normal case */ ;
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