--- stack/stack.h	2002/03/10 09:13:36	1.8
+++ stack/stack.h	2002/03/17 11:26:35	1.16
@@ -24,28 +24,52 @@
 
 /* First, define some types. */
 
+struct cons_struct;
+struct symbol_struct;
+
 /* A value of some type */
 typedef struct {
   enum {
+    empty,			/* The empty list */
     integer,
     tfloat,
     string,
     func,			/* Function pointer */
-    symb, 
-    list
+    symb,			/* Symbol */
+    tcons			/* A pair of two values */
   } type:4;			/* Type of stack element */
 
-  int gc_garb:1;
-  int gc_protect:1;
+  union {
+    struct {
+      unsigned int mark:1;	/* Used internally in the GC */
+      unsigned int protect:1;	/* Protect from GC */
+    } flag;
+    unsigned int no_gc:2;	/* Both flags as one integer */
+  } gc;				/* Garbage collector stuff */
 
   union {
     void *ptr;			/* Pointer to the content */
+    struct cons_struct *c;	/* ...or a pointer to a cons cell */
+    struct symbol_struct *sym;	/* ...or a pointer to a symbol */
     int i;			/* ...or an integer */
-    float f;
+    float f;			/* ...or a floating point number */
   } content;			/* Stores a pointer or an integer */
 
 } value;
 
+/* An item (value) on a stack */
+typedef struct stackitem_struct
+{
+  value *item;                 /* The value on the stack */
+                               /* (This is never NULL) */
+  struct stackitem_struct *next; /* Next item */
+} stackitem;
+
+typedef struct cons_struct {	/* A pair of two values */
+  value *car;
+  value *cdr;
+} pair;
+
 /* A symbol with a name and possible value */
 /* (These do not need reference counters, they are kept unique by
    hashing.) */
@@ -58,21 +82,10 @@
 /* A type for a hash table for symbols */
 typedef symbol *hashtbl[HASHTBLSIZE]; /* Hash table declaration */
 
-/* An item (value) on a stack */
-typedef struct stackitem_struct
-{
-  value *item;			/* The value on the stack */
-				/* (This is never NULL) */
-  struct stackitem_struct *next; /* Next item */
-} stackitem;
-
 /* An environment; gives access to the stack and a hash table of
    defined symbols */
 typedef struct {
-  stackitem *gc_ref;
-  int gc_limit, gc_count;
-
-  stackitem *head;		/* Head of the stack */
+  value *head;			/* Head of the stack */
   hashtbl symbols;		/* Hash table of all variable bindings */
   int err;			/* Error flag */
   char *in_string;		/* Input pending to be read */
@@ -80,6 +93,11 @@
 				   read from in_string */
   FILE *inputstream;		/* stdin or a file, most likely */
   int interactive;		/* print prompts, stack, etc */
+
+  /* Garbage Collector stuff*/
+  stackitem *gc_ref;		/* Stack of all allocated values */
+  int gc_limit;			/* Run GC when this much is allocated */
+  int gc_count;			/* Amount currently allocated */
 } environment;
 
 /* A type for pointers to external functions */
@@ -103,12 +121,12 @@
 void push_sym(environment*, const char*);
 extern void nl();
 extern void type(environment*);
-void print_h(stackitem*, int);
+void print_h(value*, int);
 extern void print_(environment*);
 extern void print(environment*);
 extern void princ_(environment*);
 extern void princ(environment*);
-void print_st(stackitem*, long);
+void print_st(value*, long);
 extern void printstack(environment*);
 extern void swap(environment*);
 extern void rot(environment*);
@@ -151,3 +169,4 @@
 extern void sx_3c3d(environment*);
 extern void sx_3e3d(environment*);
 extern void sx_646976(environment*);
+extern void then(environment*);