“stak” backwards, also “cat” like concatenate with a K

• description: stack-based with arrays and lambdas
• inspiration: Factor, K
• novel features: none but the mix of stack + array is unusual (Uia)
• example syntax
  • code (top of stack):
  • [43 0 6] 1 - ([42 -1 5])
  • [43 44 45]{x y -}:foo;[-2 0 3]foo ([45 44 42])

The end is not the end because the end of the program is whatever’s on top (the start) of the stack.

This program kinda works:

iex(4)> "[20] 3 -" |> parse |> eval
17

…although in my mind the return value should be the list [17], not the bare int 17.

More obviously buggy:

iex(5)> "[20 10 22] 3 -" |> parse |> eval
* (RuntimeError) Unexpected stack at end: [22, 10, 20]
    repl.ex:35: AstEvaluator.eval_nodes/2
    repl.ex:40: AstEvaluator.eval_nodes/2
    iex:5: (file)

This should result in [17, 7, 19] rather than an exception. Most likely I’m missing a pattern match somewhere.

I leaned heavily on an LLM (perplexity) for help with translating my ideas into Elixir code. This felt a little different from my similar experience using an LLM to help me sketch out a Go program, because the idioms of Elixir are less familiar to me and therefore I had fewer preconceived notions about what good code “should” look like.

When I ran into errors the LLM was not very helpful. This could have been because of the just slightly-off-the-beaten-path language (which has lists) compared to what’s presumably more represented in the training data (simple stack-based evaluators). I’d try to debug an issue using the LLM and it would make up problems that weren’t there.

In some ways this is actually a good thing, because it more quickly exposes the limitations of the LLM as a coding assistant compared to working with a much more idiomatic and popular language like Go, where the errors will show up later and be more subtle (and harder to debug).

Currently it’s only functional as a postfix calculator with no-op brackets around the scalar integer arguments, so the to-do list is long and many fundamental features remain:

• debug list construction
• debug ast evaluation
• add functions
• add names

• how to auto-recompile while developing in IEx