Someone incorrectly ‘improved’ Rich’s reply to a StackOverflow question in 2020. I don’t know enough about the site to fix it. Maybe someone who does can. It’s just the “seq s” which should be “seqs” and, I think, the ‘not’ has been bolded when it was not. https://stackoverflow.com/questions/1641626/how-to-convert-lazy-sequence-to-non-lazy-in-clojure. It’s interesting that someone can tweak a response on there and change what one has posted (minor as it is in this case). I’m a bit OCD and would be annoyed to find answers I made changed in this way.

SOLVED My MVE was failing because there is no generator for fn?. My real problem was a hidden recursion in my base case. Once I pulled that out everything is fine. I’m just learning clojure.spec.alpha. I’m writing specs for testing a compiler back end (LPython [sic], ). The input to the back end is a recursively defined tree structure. I want to generate test cases. I present below an MVE that illustrates my question. I’m able to check (`s/valid?`, s/conform) hand-written trees. The generator, however, only occasionally produces usable results. Most of the time, it throws an exception. However, it occasionally does produce a usable example, so I am not completely dumb! What can I do to improve the following so that it produces usable examples more frequently? Or should I be doing things some other way, completely? I will be grateful for any guidance!

(ns asr.core
  (:gen-class)
  (:require [clojure.spec.alpha     :as s]
            [clojure.spec.gen.alpha :as gen] ))

(s/def ::recur-tree-mve
    (s/or :base  (s/or :i integer? :f fn?)
          :recur (s/map-of #{:left :right :op} ::recur-tree-mve)))

  (s/valid? ::recur-tree-mve 42)
  (s/valid? ::recur-tree-mve {:left {:left 5, :right 8}, :op +, :right 2})

  (def RECURSION-LIMIT 1) ; careful!
  ;; for interactive testing in CIDER:
  ;; C-x C-e after the closing parenthesis
  (binding [s/*recursion-limit* RECURSION-LIMIT]
    (->> ::recur-tree-mve
         s/gen
         gen/generate ))

(with-redefs [conj dissoc] (conj {:a 1} :a))
=> {}
(with-redefs [inc dec] (inc 1))
=> 2
(with-redefs [inc dec] (@#'inc 1))
=> 0