commit e0a2599d8debf2d6871eb121bc4af8345fbfa62c
Author: Elf M. Sternberg <elf.sternberg@gmail.com>
Date:   Sat Dec 10 17:00:58 2016 -0800

    Initial check-in.

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d9d39f2
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,18 @@
+*#
+.#*
+*~
+*.orig
+npm-debug.log
+package.yml
+node_modules/*
+tmp/
+bin/_mocha
+bin/mocha
+bin/escodegen
+bin/esgenerate
+test-reports.xml
+LisperatorLanguage
+src/test.js
+src/test.coffee
+notes/
+build/
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..802a300
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,7 @@
+project("Collector")
+
+list(APPEND CMAKE_C_FLAGS "-std=c99 ${CMAKE_C_FLAGS} -g -ftest-coverage -fprofile-arcs")
+
+add_executable(collector
+    src/collector.c)
+
diff --git a/src/collector.c b/src/collector.c
new file mode 100644
index 0000000..4daa110
--- /dev/null
+++ b/src/collector.c
@@ -0,0 +1,238 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX_STACK 256
+#define MAX_BARRIER 8
+
+typedef enum {
+  OBJ_INT,
+  OBJ_PAIR
+} ObjectType;
+
+typedef struct sObject {
+  unsigned char marked;
+  struct sObject* next;
+  ObjectType type;
+  union {
+    int value;
+    struct {
+      struct sObject* head;
+      struct sObject* tail;
+    };
+  };
+} Object;
+
+typedef struct {
+  Object* stack[MAX_STACK];
+  Object* root;
+  int stackSize;
+  int numObjects;
+  int maxObjects;
+} VM;
+
+void assert(int condition, const char* message) {
+  if (!condition) {
+    printf("%s\n", message);
+    exit(1);
+  }
+}
+
+VM* newVM() {
+  VM* vm = malloc(sizeof(VM));
+  vm->stackSize = 0;
+  vm->numObjects = 0;
+  vm->maxObjects = MAX_BARRIER;
+  return vm;
+}
+
+void push(VM* vm, Object* value) {
+  assert(vm->stackSize < MAX_STACK, "Stack overflow!");
+  vm->stack[vm->stackSize++] = value;
+}
+
+Object* pop(VM* vm) {
+  assert(vm->stackSize > 0, "Stack underflow!");
+  return vm->stack[--(vm->stackSize)];
+}
+
+void mark(Object* object) {
+  if (object->marked) {
+    return;
+  }
+  
+  object->marked = 1;
+  if (object->type == OBJ_PAIR) {
+    mark(object->head);
+    mark(object->tail);
+  }
+}
+
+void markAll(VM* vm) {
+  for(int i = 0; i < vm->stackSize; i++) {
+    mark(vm->stack[i]);
+  }
+}
+
+void sweep(VM* vm) {
+  Object** object = &vm->root;
+  while (*object) {
+    if (!(*object)->marked) {
+      Object* unreached = *object;
+      *object = unreached->next;
+      vm->numObjects--;
+      free(unreached);
+    } else {
+      (*object)->marked = 0;
+      object = &(*object)->next;
+    }
+  }
+}
+
+void gc(VM* vm) {
+  int numObjects = vm->numObjects;
+  markAll(vm);
+  sweep(vm);
+  vm->maxObjects = vm->numObjects * 2;
+  printf("Collected %d objects, %d remaining.\n", numObjects - vm->numObjects,
+         vm->numObjects);
+}
+
+Object *newObject(VM* vm, ObjectType type) {
+  if (vm->numObjects == vm->maxObjects) {
+    gc(vm);
+  }
+
+  Object* object = malloc(sizeof(Object));
+  object->marked = 0;
+  object->type = type;
+  object->next = vm->root;
+  vm->root = object;
+  vm->numObjects++;
+  return object;
+}
+
+Object* pushInt(VM* vm, int value) {
+  Object* object = newObject(vm, OBJ_INT);
+  object->value = value;
+  push(vm, object);
+  return object;
+}
+
+Object* pushPair(VM* vm) {
+  Object* object = newObject(vm, OBJ_PAIR);
+  object->head = pop(vm);
+  object->tail = pop(vm);
+  push(vm, object);
+  return object;
+}
+  
+void freeVM(VM *vm) {
+  vm->stackSize = 0;
+  gc(vm);
+  free(vm);
+}
+
+void objectPrint(Object* object) {
+  switch(object->type) {
+  case OBJ_INT:
+    printf("%d\n", object->value);
+    break;
+
+  case OBJ_PAIR:
+    printf("(");
+    objectPrint(object->head);
+    printf(", ");
+    objectPrint(object->tail);
+    printf(")");
+    break;
+  }
+}
+
+void test1() {
+  printf("Test 1: Objects on stack are preserved.\n");
+  VM* vm = newVM();
+  pushInt(vm, 1);
+  pushInt(vm, 2);
+
+  gc(vm);
+  assert(vm->numObjects == 2, "Should have preserved objects.");
+  freeVM(vm);
+}
+
+void test2() {
+  printf("Test 2: Unreached objects are collected.\n");
+  VM* vm = newVM();
+  pushInt(vm, 1);
+  pushInt(vm, 2);
+  pop(vm);
+  pop(vm);
+
+  gc(vm);
+  assert(vm->numObjects == 0, "Should have collected objects.");
+  freeVM(vm);
+}
+
+void test3() {
+  printf("Test 3: Reach nested objects.\n");
+  VM* vm = newVM();
+  pushInt(vm, 1);
+  pushInt(vm, 2);
+  pushPair(vm);
+  pushInt(vm, 3);
+  pushInt(vm, 4);
+  pushPair(vm);
+  pushPair(vm);
+
+  gc(vm);
+  assert(vm->numObjects == 7, "Should have reached objects.");
+  freeVM(vm);
+}
+
+void test4() {
+  printf("Test 4: Handle cycles.\n");
+  VM* vm = newVM();
+  pushInt(vm, 1);
+  pushInt(vm, 2);
+  Object* a = pushPair(vm);
+  pushInt(vm, 3);
+  pushInt(vm, 4);
+  Object* b = pushPair(vm);
+
+  /* Set up a cycle, and also make 2 and 4 unreachable and collectible. */
+  a->tail = b;
+  b->tail = a;
+
+  gc(vm);
+  assert(vm->numObjects == 4, "Should have collected objects.");
+  freeVM(vm);
+}
+
+void perfTest() {
+  printf("Performance Test.\n");
+  VM* vm = newVM();
+
+  for (int i = 0; i < 1000; i++) {
+    for (int j = 0; j < 20; j++) {
+      pushInt(vm, i);
+    }
+
+    for (int k = 0; k < 20; k++) {
+      pop(vm);
+    }
+  }
+  freeVM(vm);
+}
+
+int main(int argc, const char * argv[]) {
+  test1();
+  test2();
+  test3();
+  test4();
+  perfTest();
+
+  return 0;
+}
+
+
+
+