Clojurians Log v2

Interesting, thanks Sean! Will play with this more

Hey Sean, tried playing with this a bit: Based on trial, it seems like interleave should work as a recursive macro too (as it only works on the forms)

(defmacro rec-interleave [s1 s2]
  `(cons-stream (car-stream ~s1)
                (rec-interleave ~s2 (cdr-stream ~s1))))

(macroexpand '(rec-interleave integers integers))

=> [(chp3/car-stream integers) (chp3/my-delay (chp3/rec-interleave integers (chp3/cdr-stream integers)))]

Execution error (NoClassDefFoundError) at nrepl.middleware.interruptible-eval/evaluate (interruptible_eval.clj:79).
Could not initialize class clojure.lang.Compiler$CompilerException

@stopachka My first suspicion would be that it is an infinite evaluation. But I always advise debugging things in a plain REPL, without nREPL and all that other stuff that tries to "help" manage evaluation and display of results.

Without seeing a self-contained, repeatable project up on GitHub containing this code, it would be hard for me to suggest anything further.

Thanks Sean! https://github.com/stopachka/interleave-demo-for-sean ---

Okay I think I understand why my thing is not working. Indeed it is trying to eval in a loop

I am not sure how my interleave is different from the trial one: Perhaps the big thing is the if — if doesn’t eval the the forms until runtime, while mine evals at compile time.

Just looked at this -- now I can see what the other functions/macros are -- and you're falling into the same trap I talked about above: your macroexpansion has no "bottom" at compile time so it just recursively expands until you get a stackoverflow.

The example I gave works because it is analyzing forms at compile time and so it can tell when it hits the end of a form. It wouldn't work with bound names because those are not sequence forms.

(rec-interleave integers integers) expands to [(interleave.demo/car-stream integers) (interleave.demo/my-delay (interleave.demo/rec-interleave integers (interleave.demo/cdr-stream integers)))] but in trying to evaluate that the remaining rec-interleave call is macroexpanded again and it always produces a larger form. Hence the infinite loop during evaluation.

Does that help @stopachka?

Am close but don’t quite get the difference between trial and interleave: > It wouldn’t work with bound names because those are not sequence forms. Do you mind expounding a bit? What is the difference between a bound name and a sequence form? i.e:

(defmacro trial [x]
  (if (seq x)
    `(do 
      (println ~(first x)) 
      (trial ~(rest x)))
    :done))

It does do something -- it expands it. But pay attention to what actually happens as you expand it each time:

user=> (macroexpand '(trial [1 2 3]))
(do (clojure.core/println 1) (user/trial (2 3)))
user=> (macroexpand '(trial [2 3]))
(do (clojure.core/println 2) (user/trial (3)))
user=> (macroexpand '(trial [3]))
(do (clojure.core/println 3) (user/trial ()))
user=> (macroexpand '(trial []))
:done
user=> 

It's processing the form [1 2 3] at compile-time, not the runtime value [1 2 3].

And the form shrinks on each expansion so it bottoms out.

But in

user=> (def x [1 2 3])
#'user/x
user=> (macroexpand '(trial x))
Syntax error macroexpanding trial at (REPL:12:1).
Don't know how to create ISeq from: clojure.lang.Symbol
user=> 

Macros work on code, not values.

Aah I see! So if we had passed in (trial [foo bar]) It would do something like print ’foo ’bar --- Oky doke this makes a lot of sense. Thanks Sean!