An epiphany!

3. a sudden, intuitive perception of or insight into the reality or essential meaning of something, usually initiated by some simple, homely, or commonplace occurrence or experience.

I actually thanked my mother for dragging my out on a shopping expedition today, because I figured out sometime a ways "down" my todo list: implementing control flow in tpsh. I guess you can take the programmer away from the code, but you can't take the code away from programmer ^_^ ^_^ ^_^.


Earlier I recorded that the goal was for tpsh to use a queue of commands to execute rather then going by lines, the idea being:

`cmd1; cmd2; cmd3`

would parse into a list like '(cmd1, cmd2, cmd3') which tpsh would then walk, eval, and execute the result in sequence (i.e. first in, first out). Then it occurred to me, if the shell will go that route for lexical reasons: why not implement the shells control flow operators as keywords that manipulate that queue directly? So that conceptually, a shell snippet like:

cmd0
if [ expr ]; then
  cmd1
  cmd2
else
  cmd3
  cmd4
fi
cmd5

would be inserted into the queue in a suitable manor and passed to the call back, so if the queue looked something like this:

( cmd0, if [ expr ], cmd1, cmd2, else, cmd3, cmd4, fi, cmd5 )

the call back would receive that relevant portion of the queue, (i.e. queue₁ through queue₇), evaluate the test and return the appropriate portion to be spliced into the queue, in this case:


( cmd0, cmd1, cmd2, cmd5 ) or ( cmd0, cmd3, cmd4, cmd5 )

depending on whether `[ expr ]` evaluated as true or false.



Damn, this so makes me want to straighten up the necessary parts of tpsh... now if only I didn't have to work tomorrow from morning to whenever I drop over undead, or pass out lol. These kinds of things have always fascinated me about programming, but life has never offered much chance to study compilers, virtual machines, and interpretors... let along create something like tpsh, that requires implementing a scripting language :\. The one good thing, despite the ups/downs and expressiveness of sh script, it's really an easy language for a human to understand.