with-output-to-string fix for uLisp

string-stream-fix.diff

diff --git a/c99/ulisp.c b/c99/ulisp.c
index 4318099..52a997e 100644
--- a/c99/ulisp.c
+++ b/c99/ulisp.c
@@ -275,6 +275,7 @@ object *GCStack = NULL;
 object *GlobalString;
 object *GlobalStringTail;
 int GlobalStringIndex = 0;
+object *GlobalStringStreamTail = NULL;
 uint8_t PrintCount = 0;
 uint8_t BreakLevel = 0;
 char LastChar = 0;
@@ -332,6 +333,7 @@ bool keywordp (object *obj);
 int stringcompare (object *args, bool lt, bool gt, bool eq);
 object *eval (object *form, object *env);
 void pstr (char c);
+void pstrstream (char c);
 object *findpair (object *var, object *env);
 char *lookupdoc (builtin_t name);
 char *cstring (object *form, char *buffer, int buflen);
@@ -535,7 +537,11 @@ void errorsub (symbol_t fname, const char *string) {
   pfstring(string, pserial);
 }
 
-void errorend () { GCStack = NULL; longjmp(*handler, 1); }
+void errorend () {
+  GCStack = NULL;
+  GlobalStringStreamTail = NULL;
+  longjmp(*handler, 1);
+}
 
 /*
   errorsym - prints an error message and reenters the REPL.
@@ -616,6 +618,8 @@ const char indexrange[] = "index out of range";
 const char canttakecar[] = "can't take car";
 const char canttakecdr[] = "can't take cdr";
 const char unknownstreamtype[] = "unknown stream type";
+const char streamalreadyopen[] = "stream already open";
+const char streamclosed[] = "stream has been closed";
 
 // Set up workspace
 
@@ -2008,7 +2012,7 @@ uint8_t nthchar (object *string, int n) {
 }
 
 /*
-  gstr - reads a character from a string stream
+  gstr - reads a character from the global string
 */
 int gstr () {
   if (LastChar) {
@@ -2022,12 +2026,19 @@ int gstr () {
 }
 
 /*
-  pstr - prints a character to a string stream
+  pstr - prints a character to the global string
 */
 void pstr (char c) {
   buildstring(c, &GlobalStringTail);
 }
 
+/*
+  pstrstream - prints a character to a string stream
+*/
+void pstrstream (char c) {
+  buildstring(c, &GlobalStringStreamTail);
+}
+
 /*
   lispstring - converts a C string to a Lisp string
 */
@@ -2705,7 +2716,8 @@ pfun_t pfun_serial (uint8_t address) {
 
 pfun_t pfun_string (uint8_t address) {
   (void) address;
-  return pstr;
+  if (GlobalStringStreamTail == NULL) error2(streamclosed);
+  return pstrstream;
 }
 
 pfun_t pfun_sd (uint8_t address) {
@@ -3450,14 +3462,17 @@ object *sp_time (object *args, object *env) {
 */
 object *sp_withoutputtostring (object *args, object *env) {
   object *params = checkarguments(args, 1, 1);
+  if (GlobalStringStreamTail != NULL) error2(streamalreadyopen);
   object *var = first(params);
   object *pair = cons(var, stream(STRINGSTREAM, 0));
   push(pair,env);
-  object *string = startstring();
+  object *string = newstring();
+  GlobalStringStreamTail = string;
   protect(string);
   object *forms = cdr(args);
   eval(tf_progn(forms,env), env);
   unprotect();
+  GlobalStringStreamTail = NULL;
   return string;
 }