becavalier / quickforth

(POC) A forth dialect prototype with its VM.

QuickForth

A simple forth dialect prototype with its VM, just for experimental purpose.

* You can continue to extend the function of this VM if you will.

Can only be used under Linux X86-64.

Compile

make  # the binary will be compiled into the "build" folder.

Modes

• REPL:

➜  Forthress git:(master) ✗ ./build/vm
> 1
> 2
> +
> .S
3
> exit

• Interpreter:

➜  Forthress git:(master) ✗ ./build/vm forth_discr.fth
-8

Concepts

• Native Word:

Word provided by the VM.

• Colon Word:

Word constituted by a series of Native Words (need docol to control the flow).

Format: prologue: xt_docol, epilogue: xt_ret;

• Control Flow:

Execution Sequences (Native Words):

+------+    +------+ 
| word | -> | word | ...
+------+    +------+
    ^           ^
    w           pc

Execution Sequences (Colon Words):

+------+    +------+ 
| word | -> | word | ...
+------+    +------+
    |           ^
    |           pc (saved in rstack)
+------+    +------+     |
| word | -> | word | ... |
+------+    +------+     | 
    ^           ^        |
    w           pc (new position) 

Architecture

• Word:

|---------------------->  header (exclude private word)  <---------------------|
+---------------------+----------------+-----------------+---------------------+
| next word addr (dq) | label (string) | (reserved byte) | implementation addr |
+---------------------+----------------+-----------------+---------------------+

• Dictionary:

 (head)                               (tail)             (.bss)
+------+    +------+     +------+    +------+    +--------------------+
| word | -> | word | ... | word | -> | word | -> | dynamic_colon_stub | -> (dynamic words)
+------+    +------+     +------+    +------+    +--------------------+
                                                     
    +--------------------+        +-------------------------------------+
... | dynamic_colon_stub | ... => | next effective address (dq) | words | ... 
    +--------------------+        +-------------------------------------+
                                                  |--------------|--------^

• Opcode (For inner interpreter, saving the operation and immediates of each dynamic colon word):

+----------------+-------------------+
| opcode (qword) | immediate (qword) |
+----------------+-------------------+