diff --git a/src/apfl.h b/src/apfl.h
index f2edde6..d6f4251 100644
--- a/src/apfl.h
+++ b/src/apfl.h
@@ -142,6 +142,7 @@ bool apfl_format_put_hexbyte(struct apfl_format_writer, unsigned char);
 bool apfl_format_put_pos(struct apfl_format_writer, struct apfl_position);
 bool apfl_format_put_indent(struct apfl_format_writer, unsigned);
 bool apfl_format_put_number(struct apfl_format_writer, apfl_number);
+bool apfl_format_put_poiner(struct apfl_format_writer, void *);
 
 // Tokens
 
diff --git a/src/format.c b/src/format.c
index 6b52860..ff5c7e3 100644
--- a/src/format.c
+++ b/src/format.c
@@ -114,3 +114,14 @@ apfl_format_put_number(struct apfl_format_writer w, apfl_number number)
     }
     return true;
 }
+
+#define PUT_POINTER_BUFSIZE 34 // Enough for "0x" + 32 hex digits, so enough for a 128-bit pointer.
+
+bool
+apfl_format_put_poiner(struct apfl_format_writer w, void *ptr)
+{
+    char buf[PUT_POINTER_BUFSIZE];
+    size_t len = snprintf(buf, PUT_POINTER_BUFSIZE, "%p", ptr);
+    assert(len < PUT_POINTER_BUFSIZE);
+    return write(w, buf, len);
+}
diff --git a/src/gc.c b/src/gc.c
index 67be04f..b1dd3f7 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -434,7 +434,7 @@ sweep(struct gc *gc)
 }
 
 #ifdef GC_DEBUG_DUMP_GRAPH_ON_COLLECT
-# define DUMP_ON_COLLECT() apfl_gc_debug_dump_graph(gc, stderr)
+# define DUMP_ON_COLLECT() apfl_gc_debug_dump_graph(gc, apfl_format_file_writer(stderr))
 #else
 # define DUMP_ON_COLLECT()
 #endif
@@ -517,30 +517,50 @@ type_to_string(enum gc_type type)
     return "???";
 }
 
+struct dump_graph_roots_visitor_data {
+    struct apfl_format_writer w;
+    bool success;
+};
+
 static void
 dump_graph_roots_visitor(void *opaque, struct gc_object *obj)
 {
-    FILE *out = opaque;
-    fprintf(out, "ROOTS -> obj_%p;\n", (void *)obj);
+    struct dump_graph_roots_visitor_data *data = opaque;
+    data->success = data->success
+        && apfl_format_put_string(data->w, "  ROOTS -> obj_")
+        && apfl_format_put_poiner(data->w, (void *)obj)
+        && apfl_format_put_string(data->w, "\n");
 }
 
 struct dump_graph_visitor_data {
-    FILE *out;
+    struct apfl_format_writer w;
     struct gc_object *parent;
+    bool success;
 };
 
 static void
 dump_graph_visitor(void *opaque, struct gc_object *obj)
 {
     struct dump_graph_visitor_data *data = opaque;
-    fprintf(data->out, "obj_%p -> obj_%p\n", (void *)data->parent, (void *)obj);
+    data->success = data->success
+        && apfl_format_put_string(data->w, "  obj_")
+        && apfl_format_put_poiner(data->w, (void *)data->parent)
+        && apfl_format_put_string(data->w, " -> obj_")
+        && apfl_format_put_poiner(data->w, (void *)obj)
+        && apfl_format_put_string(data->w, "\n");
 }
 
-void
-apfl_gc_debug_dump_graph(struct gc *gc, FILE *out)
+bool
+apfl_gc_debug_dump_graph(struct gc *gc, struct apfl_format_writer w)
 {
-    fprintf(out, "digraph G {\n");
-    visit_roots(gc, dump_graph_roots_visitor, out);
+    FMT_TRY(apfl_format_put_string(w, "digraph G {\n"));
+
+    struct dump_graph_roots_visitor_data roots_visitor_data = {
+        .w = w,
+        .success = true,
+    };
+    visit_roots(gc, dump_graph_roots_visitor, &roots_visitor_data);
+    FMT_TRY(roots_visitor_data.success);
 
     for (struct gc_block *block = gc->block; block != NULL; block = block->next) {
         int counts[4] = {0, 0, 0, 0};
@@ -552,36 +572,57 @@ apfl_gc_debug_dump_graph(struct gc *gc, FILE *out)
                 continue;
             }
 
-            fprintf(out, "blk_%p -> obj_%p;\n", (void *)block, (void *)obj);
-            fprintf(
-                out,
-                "obj_%p [style=filled,fillcolor=%s,fontcolor=%s,label=\"Object %p\\ntype: %s\"];\n",
-                (void *)obj,
-                dump_graph_bgcolor(obj->status),
-                dump_graph_fgcolor(obj->status),
-                (void *)obj,
-                type_to_string(obj->type)
-            );
+            FMT_TRY(apfl_format_put_string(w, "  blk_"));
+            FMT_TRY(apfl_format_put_poiner(w, (void *)block));
+            FMT_TRY(apfl_format_put_string(w, " -> obj_"));
+            FMT_TRY(apfl_format_put_poiner(w, (void *)obj));
+            FMT_TRY(apfl_format_put_string(w, "\n"));
 
-            visit_children(obj, dump_graph_visitor, &(struct dump_graph_visitor_data) {
-                .out = out,
+
+            FMT_TRY(apfl_format_put_string(w, "  obj_"));
+            FMT_TRY(apfl_format_put_poiner(w, (void *)obj));
+            FMT_TRY(apfl_format_put_string(w, "[style=filled,fillcolor="));
+            FMT_TRY(apfl_format_put_string(w, dump_graph_bgcolor(obj->status)));
+            FMT_TRY(apfl_format_put_string(w, ",fontcolor="));
+            FMT_TRY(apfl_format_put_string(w, dump_graph_fgcolor(obj->status)));
+            FMT_TRY(apfl_format_put_string(w, ",label=\"Object "));
+            FMT_TRY(apfl_format_put_poiner(w, (void *)obj));
+            FMT_TRY(apfl_format_put_string(w, "\\ntype: "));
+            FMT_TRY(apfl_format_put_string(w, type_to_string(obj->type)));
+            FMT_TRY(apfl_format_put_string(w, "\"];\n"));
+
+            struct dump_graph_visitor_data visitor_data = {
+                .w = w,
                 .parent = obj,
-            });
+                .success = true,
+            };
+
+            visit_children(obj, dump_graph_visitor, &visitor_data);
+            FMT_TRY(visitor_data.success);
         }
 
-        fprintf(out, "BLOCKS -> blk_%p;\n", (void *)block);
-        fprintf(
-            out,
-            "blk_%p [label=\"Block %p\\nfree %d, black %d, grey %d, white %d\"];\n",
-            (void *)block,
-            (void *)block,
-            counts[GC_STATUS_FREE],
-            counts[GC_STATUS_BLACK],
-            counts[GC_STATUS_GREY],
-            counts[GC_STATUS_WHITE]
-        );
+        FMT_TRY(apfl_format_put_string(w, "  BLOCKS -> blk_"));
+        FMT_TRY(apfl_format_put_poiner(w, (void *)block));
+        FMT_TRY(apfl_format_put_string(w, ";\n"));
+
+        FMT_TRY(apfl_format_put_string(w, "  blk_"));
+        FMT_TRY(apfl_format_put_poiner(w, (void *)block));
+        FMT_TRY(apfl_format_put_string(w, " [label=\"Block "));
+        FMT_TRY(apfl_format_put_poiner(w, (void *)block));
+        FMT_TRY(apfl_format_put_string(w, "\\nfree "));
+        FMT_TRY(apfl_format_put_int(w, counts[GC_STATUS_FREE]));
+        FMT_TRY(apfl_format_put_string(w, ", black "));
+        FMT_TRY(apfl_format_put_int(w, counts[GC_STATUS_BLACK]));
+        FMT_TRY(apfl_format_put_string(w, ", grey "));
+        FMT_TRY(apfl_format_put_int(w, counts[GC_STATUS_GREY]));
+        FMT_TRY(apfl_format_put_string(w, ", white "));
+        FMT_TRY(apfl_format_put_int(w, counts[GC_STATUS_WHITE]));
+        FMT_TRY(apfl_format_put_string(w, "\"];\n"));
     }
-    fprintf(out, "}\n");
+
+    FMT_TRY(apfl_format_put_string(w, "}\n"));
+
+    return true;
 }
 
 void
diff --git a/src/gc.h b/src/gc.h
index 168b868..8573280 100644
--- a/src/gc.h
+++ b/src/gc.h
@@ -8,6 +8,7 @@ extern "C" {
 #include <stdint.h>
 
 #include "apfl.h"
+#include "format.h"
 
 #include "hashmap.h"
 
@@ -68,7 +69,7 @@ struct gc_object *apfl_gc_object_from_ptr(void *, enum gc_type);
 void apfl_gc_init(struct gc *, struct apfl_allocator, gc_roots_getter, void *roots_getter_opaque);
 void apfl_gc_deinit(struct gc *);
 
-void apfl_gc_debug_dump_graph(struct gc *, FILE *);
+bool apfl_gc_debug_dump_graph(struct gc *, struct apfl_format_writer);
 
 size_t apfl_gc_tmproots_begin(struct gc *gc);
 void apfl_gc_tmproots_restore(struct gc *gc, size_t);
diff --git a/src/globals.c b/src/globals.c
index 2c501f4..d234588 100644
--- a/src/globals.c
+++ b/src/globals.c
@@ -310,6 +310,25 @@ impl_while(apfl_ctx ctx)
     }
 }
 
+static void
+impl_gc(apfl_ctx ctx)
+{
+    ONE_ARG(ctx, "gc");
+    apfl_tostring(ctx, -1);
+    struct apfl_string_view sv = apfl_get_string(ctx, -1);
+
+    if (apfl_string_eq(sv, "dump")) {
+        struct apfl_format_writer w = apfl_get_output_writer(ctx);
+        TRY_FORMAT(ctx, apfl_gc_debug_dump_graph(&ctx->gc, w));
+    } else if (apfl_string_eq(sv, "collect")) {
+        apfl_gc_full(&ctx->gc);
+    } else {
+        apfl_raise_const_error(ctx, APFL_RESULT_ERR, "Unknown gc command");
+    }
+
+    apfl_drop(ctx, -1);
+}
+
 static const struct global_def globals[] = {
     {"if", impl_if},
     {"==", impl_eq},
@@ -325,6 +344,7 @@ static const struct global_def globals[] = {
     {"len", len},
     {"type", type},
     {"while", impl_while},
+    {"gc", impl_gc},
     {NULL, NULL},
 };