VM: added definitions for init, push, and pop

vm.c

@@ -0,0 +1,37 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "vm.h"
+
+struct virtualMachine *initVM() {
+  struct virtualMachine *vm = malloc(sizeof(struct virtualMachine));
+  vm->stackSize = 0;
+  return vm;
+}
+
+void push(struct virtualMachine *vm, struct garbageObject *value) {
+  if (vm->stackSize >= STACK_MAX) {
+    fprintf(stderr, "ERROR: push(): Refusing to overflow the stack!\n");
+    // FIXME: Must free memory before exiting
+    exit(-1);
+  }
+  vm->stack[vm->stackSize++] = value;
+}
+
+struct garbageObject *pop(struct virtualMachine *vm) {
+  if (vm->stackSize < 0) {
+    fprintf(stderr,
+            "ERROR: pop(): Stack underflow - stack size cannot be negative!");
+    // FIXME: Must free memory before exiting
+    exit(-1);
+  }
+
+  return vm->stack[--vm->stackSize];
+}
+
+struct garbageObject *initGarbage(struct virtualMachine *vm,
+                                  enum garbageData type) {
+  struct garbageObject *obj = malloc(sizeof(struct garbageObject));
+  obj->type = type;
+  return obj;
+}