Re: [Maxima-discuss] Basic question on paths (for luatree.{mac, lisp, lua})

[Eduardo O. <edu...@gm...>]

On Fri, 5 Aug 2022 at 12:45, Robert Dodier <rob...@gm...> wrote:

> On Thu, Aug 4, 2022 at 8:56 PM Eduardo Ochs <edu...@gm...> wrote:
>
> > Problem solved - with:
> >   luatreedir    : pathname_directory(load_pathname);
> > Sorry for the noise!
> > The program is here:
> >   http://angg.twu.net/eev-maxima.html#luatree
> >   https://github.com/edrx/luatree/#introduction
>
> Eduardo, thanks for the message, that looks interesting. I like the
> style of the tree diagram that's printed. I see part of the program is
> Maxima, part Lisp, part Lua. Can you say a little bit about how the
> different parts fit together here?
>
> One approach to getting diagrams generated by Maxima is to output
> stuff in a format understood by Graphviz, and then use one of the
> GraphViz programs (I know there's dot, I forget the others) to render
> it. Dunno if it's possible to get ASCII art in the same form you
> showed. I've worked with Maxima + GraphViz to visualize function call
> graphs, it's not hard. I can sketch out that approach if you're
> interested.
>
> best,
>
> Robert
>

 Hi Robert!

I think that I found a way to answer your question that makes the main
idea look portable to other language. Let me try.

I usually program using REPLs from Emacs, with this:

  http://angg.twu.net/eepitch.html

My favorite programming language is Lua and my init file for Lua has
lots of functions and classes that I use often in throwaway programs.
If I just start a Lua REPL and type this in it,

  foo = {[0]="+", {[0]="*", "2", "3"}, {[0]="/", "4", "5"}, 6}
  print(SynTree.from(foo))

the first line sets foo to an associative table that I interpret as a
tree as:

  2*3 + 4/5 + 6

and the second line converts it to an object of the class SynTree in a
certain way and prints it using the __tostring method of the SynTree
class. What we see in the REPL buffer is this:

  Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
  > foo = {[0]="+", {[0]="*", "2", "3"}, {[0]="/", "4", "5"}, 6}
  > print(SynTree.from(foo))
  +_____._____.
  |     |     |
  *__.  /__.  6
  |  |  |  |
  2  3  4  5
  >

The first version of my luatree.lua just read stdin, interpreted it as
a Lua expression, and ran something like this:

  print(SynTree.from(expressionreadfromstdin))

Then at some point I rewrote luatree.lua to make it self-contained,
i.e., independent of my init file, and it became this:

  http://angg.twu.net/luatree/luatree.lua.html

Note that at the end of luatree.lua there is a multi-line comment
containing this test,

  echo '{[0]="[", {[0]="/", "x", "y"}, "33"}' \
    | ./luatree.lua

that outputs this when I run it:

  [_____.
  |     |
  /__.  33
  |  |
  x  y

The function luatree1d in

  http://angg.twu.net/luatree/luatree.mac.html

receives a Maxima object and returns a string that is a
one-dimensional representation of a tree in Lua syntax - like the

  '{[0]="[", {[0]="/", "x", "y"}, "33"}'

in the "echo" above - and the function luatree, that is defined in
luatree.mac as:

  luatree : lambda([o], print(luatree_lua(luatree1d(o))), "");

calls luatree_lua to convert the 1D representation of a tree into a 2D
representation... and luatree_lua is defined in

  http://angg.twu.net/luatree/luatree.lisp.html

as:

  (require :asdf)

  (defun luatree-lua (bigstr)
    (with-input-from-string
     (s bigstr)
     (reduce (lambda (a b) (format nil "~a~%~a" a b))
             (uiop:run-program
              (concatenate 'string #$luatreedir$ "luatree.lua")
              :input s :output :lines))))

  (defmfun $luatree_lua (str) (luatree-lua str))

This is my first Common Lisp program ever, and I had to ask for help
on IRC channels a lot to find this way to use uiop:run-program to pipe
a string through luatree.lua.

The class SynTree in luatree.lua builds the 2D representation of a
"syntax tree" by manipulation ascii rectangles that are objects of the
class Rect. Here is a demo that creates two Rect objects in a very
low-level way and then "concatenates" them:

  Lua 5.1.5  Copyright (C) 1994-2012 Lua.org, PUC-Rio
  > r1 = Rect({"a", "bb", "ccc"})
  > r2 = Rect({"dd", "e"})
  > print(r1..r2)
  a  dd
  bb e
  ccc
  >

Lua sees both r1 and r2 as tables, and the usual concatenation
operator - the ".." - doesn't know how to handle concatenation of
tables, so it calls the function __concat in the metatable of r1. I
don't know how to do something like that in Common Lisp, but I plan to
learn how to do that when I grow up. Help welcome! =P

About GraphViz: I'm interested! Please explain! =)
  Cheers,
    Eduardo