pit: TODO update

1 files changed, 43 insertions, 0 deletions

diff --git a/pit/whereweleftoff.org b/pit/whereweleftoff.org
index 3b89918..c7a5ccb 100644
--- a/pit/whereweleftoff.org
+++ b/pit/whereweleftoff.org
@@ -6,3 +6,46 @@
 - we can probably make pit_expand_macros operate in place
 - if we want to be really smart, cool, happy, rich:
   let's just make stuff translate to a little VM before it evaluates, and let's store VM programs as functions instead of sexps
+
+* little vm thing
+let's have a "program" (representation of one function) be a cons-list of instructions
+during execution, we maintain a stack of programs.
+calling a lisp function entails pushing a new "frame" to this stack
+we iterate over the frame by cdring as usual and we pop the frame when we reach the end
+
+#+begin_src pit
+(defun! add2 (x y) (+ x y 2))
+#+end_src
+
+#+begin_src pit
+[
+  (literal x)
+  (get)
+  (literal y)
+  (get)
+  (literal 2)
+  (literal +)
+  (fget)
+  (apply 3)
+]
+#+end_src
+
+#+begin_src pit
+(defun! foo (x) (* (add2 x x) 4))
+#+end_src
+
+#+begin_src pit
+[
+  (literal x)
+  (get)
+  (literal x)
+  (get)
+  (literal add2)
+  (fget)
+  (apply 2) ;; evaluating this pushes a new frame with the code for add2. next "tick" of evaluator continues in that code. once it returns, result is on the stack (for free) 
+  (literal 4)
+  (literal *)
+  (fget)
+  (apply 2)
+]
+#+end_src