Add function point for ending markov chain

continue-fn function parameter is used to supply a function, which
controls if the chain is continuing or if it has reached end. Reason for
this is to enable different kinds of chains, for example those that may
contain nil elements or other falsey items.

Author: tuturto

src/pyherc/markov.hy

@@ -23,15 +23,15 @@
 (require pyherc.macros)
 (import random)
 
-(defn chain-factory [start-elements elements]
+(defn chain-factory [start-elements elements continue-fn]
   "create factory function that can create markov chain instances"
   (fn []
     "create generator for chain"
     (defn select-next-element [elements-list]
       "select element"
-      (let [[high (max (list-comp upper [#t(element lower upper) elements-list]))]
+      (let [[high (max (list-comp upper [#t (element lower upper) elements-list]))]
             [value (.randint random 0 high)]
-            [matches (list-comp element [#t(element lower upper) elements-list]
+            [matches (list-comp element [#t (element lower upper) elements-list]
                                 (> lower value upper))]]
         (if matches
           (first (.choice random matches))
@@ -42,9 +42,7 @@
     (yield current-element)
     (while running
       (setv next-elements (get elements current-element))
-      (if next-elements
-             (setv current-element (select-next-element next-elements))
-             (setv running false))
+      (setv current-element (select-next-element next-elements))
+      (setv running (continue-fn current-element))
       (when (not running) (break))
       (yield current-element))))
-

src/pyherc/test/unit/test_markov.hy

@@ -30,7 +30,8 @@
 
 (background infinite-foo-chain
             [factory (chain-factory :start-elements [#t("foo" 1 100)]
-                                    :elements {"foo" [#t("foo" 1 100)]})]
+                                    :elements {"foo" [#t("foo" 1 100)]}
+                                    :continue-fn (fn [item] true))]
             [chain (factory)])
 
 (fact "first element of chain can be read"
@@ -45,7 +46,8 @@
 
 (background one-element-chain
             [factory (chain-factory :start-elements [#t("foo" 1 100)]
-                                    :elements {"foo" []})]
+                                    :elements {"foo" [#t(nil 1 100)]}
+                                    :continue-fn (fn [item] (not (is item nil))))]
             [chain (factory)])
 
 (fact "one element markov chain contains only one element"
@@ -58,7 +60,8 @@
 (background flip-flop-chain
             [factory (chain-factory :start-elements [#t("flip" 1 100)]
                                     :elements {"flip" [#t("flop" 1 100)]
-                                               "flop" [#t("flip" 1 100)]})]
+                                               "flop" [#t("flip" 1 100)]}
+                                    :continue-fn (fn [item] true))]
             [chain (factory)])
 
 (fact "markov chain can switch between states"
@@ -76,7 +79,8 @@
                                                "bar" [#t("foo" 1 50)
                                                       #t("baz" 51 100)]
                                                "baz" [#t("foo" 1 50)
-                                                      #t("bar" 51 100)]})]
+                                                      #t("bar" 51 100)]}
+                                    :continue-fn (fn [item] true))]
             [chain (factory)])
 
 (fact "markov chain can have multiple transitions from single element"