Add seemingly functional but hacky gc

src/evaluate.c

@@ -35,6 +35,7 @@ struct ucl_object *ucl_evaluate_builtin_form(struct ucl_state *state, struct ucl
             i++;
         }
         result = ucl_progn(fun_state, fun_forms);
+        ucl_state_delete(fun_state);
     } else {
         assert(0);
     }

src/internal.h

@@ -13,6 +13,15 @@
          item_name != NULL && iter_name != NULL && (cond); \
          iter_name = iter_name->cell.cdr, item_name = (iter_name == NULL) ? NULL : iter_name->cell.car)
 
+// TODO: Refactor this struct's location
+struct ucl_state {
+    // TODO: For garbage collection, we need references from the parent->child state
+    struct ucl_object *list;
+    struct ucl_state *parent;
+};
+
+extern struct ucl_arena *state_arena;
+
 struct ucl_object *ucl_cell_create(struct ucl_object *car, struct ucl_object *cdr);
 struct ucl_object *ucl_int_create(int integer);
 struct ucl_object *ucl_symbol_create(const char* symbol);

src/main.c

@@ -85,6 +85,7 @@ int main(int argc, const char **argv) {
             printf("\n");
 
             free(line);
+            ucl_gc();
         }
     } else {
         struct ucl_object *sexp = ucl_parse(argv[1]);

src/memory.c

@@ -1,12 +1,26 @@
 #include "uclisp.h"
 #include "internal.h"
+#include "arena.h"
 
+#include <assert.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
+#include <limits.h>
+#include <stdint.h>
+
+#ifndef UCL_STATE_ARENA_SIZE
+#define UCL_STATE_ARENA_SIZE 16
+#endif
+
+#ifndef UCL_OBJECT_ARENA_SIZE
+#define UCL_OBJECT_ARENA_SIZE (1 << 14)
+#endif
 
 static struct ucl_object *ucl_object_alloc();
 
+static struct ucl_arena *object_arena = NULL;
+
 struct ucl_object *ucl_cell_create(struct ucl_object *car, struct ucl_object *cdr)
 {
     struct ucl_object* obj = ucl_object_alloc();
@@ -67,7 +81,12 @@ struct ucl_object *ucl_special_create(ucl_lisp special)
 
 
 static struct ucl_object* ucl_object_alloc() {
-    return malloc(sizeof(struct ucl_object));
+    if (object_arena == NULL) {
+        object_arena = ucl_arena_create(sizeof(struct ucl_object), UCL_OBJECT_ARENA_SIZE);
+    }
+    struct ucl_object *obj =  ucl_arena_get(object_arena);
+    assert(obj != NULL);
+    return obj;
 }
 
 void ucl_object_delete(struct ucl_object *obj) {
@@ -77,9 +96,9 @@ void ucl_object_delete(struct ucl_object *obj) {
 
     switch (obj->type) {
         case UCL_TYPE_CELL:
-            ucl_object_delete(obj->cell.car);
+            //ucl_object_delete(obj->cell.car);
             obj->cell.car = NULL;
-            ucl_object_delete(obj->cell.cdr);
+            //ucl_object_delete(obj->cell.cdr);
             obj->cell.cdr = NULL;
             break;
         case UCL_TYPE_SYMBOL:
@@ -99,5 +118,50 @@ void ucl_object_delete(struct ucl_object *obj) {
         case UCL_TYPE_COUNT:
             break;
     }
-    free(obj);
+
+    ucl_arena_put(object_arena, obj);
+}
+
+void ucl_object_mark(struct ucl_object *obj) {
+    if (obj == NULL || obj->reachable) {
+        return;
+    }
+
+    obj->reachable = 1;
+    if (obj->type == UCL_TYPE_CELL) {
+        ucl_object_mark(obj->cell.car);
+        ucl_object_mark(obj->cell.cdr);
+    }
+}
+
+void ucl_state_mark(struct ucl_arena * arena, void *obj) {
+    (void) arena;
+    struct ucl_state *state = (struct ucl_state *) obj;
+
+    ucl_object_mark(state->list);
+}
+
+void ucl_gc_unmark(struct ucl_arena * arena, void *obj) {
+    (void) arena;
+    struct ucl_object *object = (struct ucl_object *) obj;
+    object->reachable = 0;
+}
+
+void ucl_gc_sweep(struct ucl_arena * arena, void *obj) {
+    (void) arena;
+    struct ucl_object *object = (struct ucl_object *) obj;
+    if (object->reachable == 0) {
+        // TODO: Mapping across this is broken, since this is a recursive delete
+        ucl_object_delete(object);
+    }
+}
+
+
+
+void ucl_gc() {
+    ucl_arena_map(object_arena, ucl_gc_unmark);
+
+    ucl_arena_map(state_arena, ucl_state_mark);
+
+    ucl_arena_map(object_arena, ucl_gc_sweep);
 }

src/special.c

@@ -22,6 +22,7 @@ struct ucl_object *ucl_special_let(struct ucl_state *state, struct ucl_object *a
 
         if (value->type == UCL_TYPE_ERROR) {
             // TODO cleanup
+            ucl_state_delete(let_state);
             return value;
         }
         ucl_state_put(let_state, sym->symbol, value);

src/state.c

@@ -2,22 +2,24 @@
 #include "internal.h"
 #include "state.h"
 #include "utility.h"
+#include "arena.h"
 
 #include <assert.h>
 #include <string.h>
 #include <stdlib.h>
 
 // Implements state as a giant alist
-// TODO: Consider generalizing the alist concept
 
-struct ucl_state {
-    struct ucl_object *list;
-    struct ucl_state *parent;
-};
+// TODO: Consider generalizing the alist concept
+// TODO: Rename 'state' to 'scope'
 
 #define NAME_POSITION 0
 #define DATA_POSITION 1
 
+#define STATE_ARENA_CAPACITY 32
+
+struct ucl_arena *state_arena;
+
 static struct ucl_object *ucl_state_get_cell(struct ucl_state *state, const char *name) {
     FOREACH_LIST(state->list, iter, item) {
         assert(item->type == UCL_TYPE_CELL);
@@ -57,7 +59,10 @@ void ucl_state_put(struct ucl_state *state, const char *name, struct ucl_object
 }
 
 struct ucl_state *ucl_state_create() {
-    struct ucl_state *state = malloc(sizeof(struct ucl_state));
+    if (state_arena == NULL) {
+        state_arena = ucl_arena_create(sizeof(struct ucl_state), STATE_ARENA_CAPACITY);
+    }
+    struct ucl_state *state = ucl_arena_get(state_arena);
     state->list = ucl_nil_create();
     state->parent = NULL;
     return state;
@@ -77,6 +82,7 @@ struct ucl_state *ucl_state_get_root(struct ucl_state *state) {
 }
 
 void ucl_state_delete(struct ucl_state *state) {
-    // TODO: Cleanup
-    // ucl_object_delete(state->list);
+    assert(state_arena != NULL);
+    ucl_arena_put(state_arena, state);
+    // Garbage collection will handle the objects, they are shared
 }

src/uclisp.h

@@ -21,7 +21,6 @@ struct ucl_state;
 typedef struct ucl_object *(*ucl_lisp)(struct ucl_state* state, struct ucl_object *args);
 
 struct ucl_object {
-    enum ucl_type type;
     union {
         struct ucl_cell cell;
         const char *symbol;
@@ -31,6 +30,8 @@ struct ucl_object {
         ucl_lisp builtin;
         ucl_lisp special;
     };
+    enum ucl_type type;
+    char reachable;
 };
 
 
@@ -46,4 +47,7 @@ struct ucl_object *ucl_tokenize(const char *source);
 struct ucl_object *ucl_parse(const char *sexp);
 struct ucl_object *ucl_evaluate(struct ucl_state *state, struct ucl_object *sexp);
 
+// TODO: State encapsulation is all wonky here)
+void ucl_gc();
+
 #endif

src/utility.c

@@ -77,6 +77,7 @@ struct ucl_object *ucl_list_nth(struct ucl_object *list, int n) {
 
     int length = ucl_list_length(list)->integer;
     UCL_COND_OR_RET_ERROR(length > n, "Position n >= list length in ucl_list_nth");
+    UCL_COND_OR_RET_ERROR(n >= 0, "Index to ucl_list_nth was less that zero");
 
     struct ucl_object *node = list;
     for (int i = 0; i < n; i++) {