potion #9: fix parser is not re-entrant, but still not GC safe

All the intermediate t and lhs objects in the compiler need to
be moved also while in a eval, and be checked for FWDs.

core/syntax.y

@@ -223,7 +223,7 @@ dec = < ('0' | [1-9][0-9]*) { $$ = YY_TNUM; }
         ('.' [0-9]+ { $$ = YY_TDEC; })?
         ('e' [-+] [0-9]+ { $$ = YY_TDEC })? >
 
-q1 = [']
+q1 = [']   # ' emacs highlight problems
 c1 = < (!q1 utf8)+ > { P->pbuf = potion_asm_write(P, P->pbuf, yytext, yyleng); }
 str1 = q1 { P->pbuf = potion_asm_clear(P, P->pbuf); }
        < (q1 q1 { P->pbuf = potion_asm_write(P, P->pbuf, "'", 1); } | c1)* >
@@ -294,6 +294,9 @@ arg-sep = '.' -        { P->source = PN_PUSH(P->source, PN_NUM('.')); }
 
 PN potion_parse(Potion *P, PN code, char *filename) {
   GREG *G = YY_NAME(parse_new)(P);
+  int oldyypos = P->yypos;
+  PN oldinput = P->input;
+  PN oldsource = P->source;
   P->yypos = 0;
   P->input = code;
   P->source = PN_NIL;
@@ -308,7 +311,9 @@ PN potion_parse(Potion *P, PN code, char *filename) {
   YY_NAME(parse_free)(G);
 
   code = P->source;
-  P->source = PN_NIL;
+  P->source = oldsource;
+  P->yypos = oldyypos;
+  P->input = oldinput;
   return code;
 }
 
@@ -318,6 +323,9 @@ PN potion_sig(Potion *P, char *fmt) {
   if (fmt[0] == '\0') return PN_FALSE; // empty signature, no args
 
   GREG *G = YY_NAME(parse_new)(P);
+  int oldyypos = P->yypos;
+  PN oldinput = P->input;
+  PN oldsource = P->source;
   P->yypos = 0;
   P->input = potion_byte_str(P, fmt);
   P->source = out = PN_TUP0();
@@ -332,7 +340,9 @@ PN potion_sig(Potion *P, char *fmt) {
   YY_NAME(parse_free)(G);
 
   out = P->source;
-  P->source = PN_NIL;
+  P->source = oldsource;
+  P->yypos = oldyypos;
+  P->input = oldinput;
   return out;
 }
 

test/flow/eval.pn

@@ -0,0 +1,3 @@
+# issue 9 - GC-safe re-entrant parser
+1 to 1000000(): 'x = Object()' eval.
+#=> 1000000