New iread function.

The read function no longer works like it used to on an
interactive terminal because of the support for .. and .
syntax on a top-level expression.

The iread function is provided which uses a modified syntax
that doesn't support these operators on a top-level
expression. The parser thus doesn't look one token ahead,
and so iread can return immediately.

* eval.c (eval_init): Register iread intrinsic function.

* parser.c (prime_parser):  Only push back the recently seen
token when priming for a regular Lisp read. Handle
the prime_interactive method by preparing a SECRET_ESCAPE_I
token.
(lisp_parse_impl): New static function, formed from previous
lisp_parse. Takes a boolean argument indicating interactive
mode.
(prime_parser_post): New function.
(lisp_parse): Now a wrapper for lisp_parse_impl which
passes a nil to indicate noninteractive read.
(iread): New function.

* parser.h (enum prime_parser): New member, prime_interactive.
(scrub_scanner, iread, prime_parser_post): Declared.

* parser.l (prime_scanner): Handle the prime_interactive case
the same way as prime_lisp.
(scrub_scanner): New function.

* parser.y (SECRET_ESCAPE_I): New token type.
(i_expr): New nonterminal symbol. Like n_expr, but doesn't
support dot or dotdot operators, except in nested
subexpressions.
(spec): Handle SECRET_ESCAPE_I by way of i_expr.
(sym_helper): Before freeing the token lexeme, call
scrub_scanner. If the token is registered as the scanner's
most recently seen token, the scanner must forget that
registration, because it is no longer valid.
(parse): Call prime_parser_post.

* txr.1: Documented iread.

1 files changed, 11 insertions, 0 deletions

diff --git a/parser.l b/parser.l
index 63941223..68767f7e 100644
--- a/parser.l
+++ b/parser.l
@@ -1065,6 +1065,7 @@ void prime_scanner(scanner_t *yyg, enum prime_parser prim)
 
   switch (prim) {
   case prime_lisp:
+  case prime_interactive:
     yy_push_state(SPECIAL, yyg);
     yy_push_state(NESTED, yyg);
     yy_push_state(NESTED, yyg);
@@ -1075,6 +1076,16 @@ void prime_scanner(scanner_t *yyg, enum prime_parser prim)
   }
 }
 
+void scrub_scanner(scanner_t *yyg, int yy_char, wchar_t *lexeme)
+{
+  struct yy_token *rtok = &yyextra->recent_tok;
+
+  if (rtok->yy_char == yy_char && rtok->yy_lval.lexeme == lexeme) {
+    rtok->yy_char = 0;
+    rtok->yy_lval.lexeme = 0;
+  }
+}
+
 void parser_l_init(void)
 {
   prot1(&form_to_ln_hash);