memo.md

env structure

env preserves global symbols and their bindings in Lisp world from GC.

      +--------+
      |        |
 next V        |
+----------+   |            +---------+
| Env *env |---+            |         |
+----------+            cdr V         |
      |               +-----------+   |
      +-------------->| TCELL:Obj |---+
                 vars +-----------+
                            |
                        car V (var)
                      +-----------+
            +---------| TCELL:Obj |-------+
            |         +-----------+       |
            |                             |
        car V (name)                  cdr V (val)
     +-------------+                 +---------+
     | TSYMBOL:Obj |                 |  *:Obj  |
     +-------------+                 +---------+

Like (defvar *env* (list (cons 'foo 1) (cons 'bar #\2) (cons 'baz "3"))) in Lisp.

root structure

root explicitly represents the stack-frame to preserve unbound intermediate objects in C world from GC.

1. at the top of main()

          +--------------------+
          |       main()       |
          +--------------------+
          | [0] NULL           |
          | [1] &main          |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **sexp     ]
          | [3] (Obj *) 0      |<----[ Obj **expanded ]
          |- - - - - - - - - - |
          | [4] (Obj *) -1     |
          +--------------------+
   

2. at the top of add_primitive() called from define_primitives()

          +--------------------+
    +---->|       main()       |
    |     +--------------------+
    |     | [0] NULL           |
    |     | [1] &main          |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sexp     ]
    |     | [3] (Obj *) 0      |<----[ Obj **expanded ]
    |     |- - - - - - - - - - |
    |     | [4] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |   add_primitive()  |
    |     +--------------------+
    +-----| [0] (Obj **) ?     |
          | [1] &add_primitive |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **prim     ]
          | [3] (Obj *) 0      |--+
          | [4] (Obj *) 0      |  | useless?
          | [5] (Obj *) 0      |--+
          |- - - - - - - - - - |
          | [6] (Obj *) -1     |
          +--------------------+
   

3. in add_var() called from add_primitive()

          +--------------------+
    +---->|       main()       |
    |     +--------------------+
    |     | [0] NULL           |
    |     | [1] &main          |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sexp     ]
    |     | [3] (Obj *) 0      |<----[ Obj **expanded ]
    |     |- - - - - - - - - - |
    |     | [4] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |   add_primitive()  |<--------------------------+
    |     +--------------------+                           |
    +-----| [0] (Obj **) ?     |                           |
          | [1] &add_primitive |                           |
          |- - - - - - - - - - |                           |
          | [2] (Obj *) 0      |<----[ Obj **prim     ]    |
          | [3] (Obj *) 0      |--+                        |
          | [4] (Obj *) 0      |  | useless?               |
          | [5] (Obj *) 0      |--+                        |
          |- - - - - - - - - - |                           |
          | [6] (Obj *) -1     |                           |
          +--------------------+                           |
                                                           |
          +--------------------+                           |
          |      add_var()     |                           |
          +--------------------+                           |
          | [0] (Obj **) ?     |---------------------------+
          | [1] &add_var       |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **sym      ]
          | [3] (Obj *) 0      |<----[ Obj **cell     ]
          | [4] (Obj *) 0      |<----[ Obj **tmp      ] useless?
          |- - - - - - - - - - |
          | [5] (Obj *) -1     |
          +--------------------+
   

4. in add_var_int() called from add_var()

          +--------------------+
    +---->|       main()       |
    |     +--------------------+
    |     | [0] NULL           |
    |     | [1] &main          |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sexp     ]
    |     | [3] (Obj *) 0      |<----[ Obj **expanded ]
    |     |- - - - - - - - - - |
    |     | [4] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |   add_primitive()  |<--------------------------+
    |     +--------------------+                           |
    +-----| [0] (Obj **) ?     |                           |
          | [1] &add_primitive |                           |
          |- - - - - - - - - - |                           |
          | [2] (Obj *) 0      |<----[ Obj **prim     ]    |
          | [3] (Obj *) 0      |--+                        |
          | [4] (Obj *) 0      |  | useless?               |
          | [5] (Obj *) 0      |--+                        |
          |- - - - - - - - - - |                           |
          | [6] (Obj *) -1     |                           |
          +--------------------+                           |
                                                           |
          +--------------------+                           |
    +---->|      add_var()     |                           |
    |     +--------------------+                           |
    |     | [0] (Obj **) ?     |---------------------------+
    |     | [1] &add_var       |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sym      ]
    |     | [3] (Obj *) 0      |<----[ Obj **cell     ]
    |     | [4] (Obj *) 0      |<----[ Obj **tmp      ] useless?
    |     |- - - - - - - - - - |
    |     | [5] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |    add_var_int()   |
    |     +--------------------+
    +-----| [0] (Obj **) ?     |
          | [1] &add_var_init  |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **cell     ]
          | [3] (Obj *) 0      |<----[ Obj **tmp      ]
          |- - - - - - - - - - |
          | [4] (Obj *) -1     |
          +--------------------+
   

5. in add_var() after returning from add_var_int() call

          +--------------------+
    +---->|       main()       |
    |     +--------------------+
    |     | [0] NULL           |
    |     | [1] &main          |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sexp     ]
    |     | [3] (Obj *) 0      |<----[ Obj **expanded ]
    |     |- - - - - - - - - - |
    |     | [4] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |   add_primitive()  |<--------------------------+
    |     +--------------------+                           |
    +-----| [0] (Obj **) ?     |                           |
          | [1] &add_primitive |                           |
          |- - - - - - - - - - |                           |
          | [2] (Obj *) 0      |<----[ Obj **prim     ]    |
          | [3] (Obj *) 0      |--+                        |
          | [4] (Obj *) 0      |  | useless?               |
          | [5] (Obj *) 0      |--+                        |
          |- - - - - - - - - - |                           |
          | [6] (Obj *) -1     |                           |
          +--------------------+                           |
                                                           |
          +--------------------+                           |
          |      add_var()     |                           |
          +--------------------+                           |
          | [0] (Obj **) ?     |---------------------------+
          | [1] &add_var       |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **sym      ]
          | [3] (Obj *) 0      |<----[ Obj **cell     ]
          | [4] (Obj *) 0      |<----[ Obj **tmp      ] useless?
          |- - - - - - - - - - |
          | [5] (Obj *) -1     |
          +--------------------+
   

6. in add_primitive() after returning from add_var() call

          +--------------------+
    +---->|       main()       |
    |     +--------------------+
    |     | [0] NULL           |
    |     | [1] &main          |
    |     |- - - - - - - - - - |
    |     | [2] (Obj *) 0      |<----[ Obj **sexp     ]
    |     | [3] (Obj *) 0      |<----[ Obj **expanded ]
    |     |- - - - - - - - - - |
    |     | [4] (Obj *) -1     |
    |     +--------------------+
    |
    |     +--------------------+
    |     |   add_primitive()  |
    |     +--------------------+
    +-----| [0] (Obj **) ?     |
          | [1] &add_primitive |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **prim     ]
          | [3] (Obj *) 0      |--+
          | [4] (Obj *) 0      |  | useless?
          | [5] (Obj *) 0      |--+
          |- - - - - - - - - - |
          | [6] (Obj *) -1     |
          +--------------------+
   

7. in define_primitives() after returning from each add_primitive() call

          +--------------------+
          |       main()       |
          +--------------------+
          | [0] NULL           |
          | [1] &main          |
          |- - - - - - - - - - |
          | [2] (Obj *) 0      |<----[ Obj **sexp     ]
          | [3] (Obj *) 0      |<----[ Obj **expanded ]
          |- - - - - - - - - - |
          | [4] (Obj *) -1     |
          +--------------------+