Sleeping Beauty problem: Difference between revisions

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 =={{header|Python}}==
+===Procedural===
 <lang python>from random import choice
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 Results of experiment:  Sleeping Beauty should estimate a credence of: 0.333542254953276
 </pre>
+===Functional===
+<lang python>'''Sleeping Beauty Problem'''
+from random import choice
+from itertools import repeat
+from functools import reduce
+# experiment :: IO Int -> (Int, Int) -> IO (Int, Int)
+def experiment(headsWakings):
+    '''A pair of counts updated by a coin flip.
+    '''
+    heads, wakings = headsWakings
+    return (
++ heads, 1 + wakings
+    ) if "h" == choice(["h", "t"]) else (
+        heads, 2 + wakings
+    )
+# ------------------------- TEST -------------------------
+# main :: IO ()
+def main():
+    '''Observed results from one million runs.'''
+    n = 1_000_000
+    heads, wakes = applyN(n)(
+        experiment
+    )(
+        (0, 0)
+    )
+    print(
+        f'{wakes} wakenings over {n} experiments.\n'
+    )
+    print('Sleeping Beauty should estimate credence')
+    print(f'at around {round(heads/wakes, 3)}')
+# ----------------------- GENERIC ------------------------
+# applyN :: Int -> (a -> a) -> a -> a
+def applyN(n):
+    '''n applications of f.
+       (Church numeral n).
+    '''
+    def go(f):
+        def ga(a, g):
+            return g(a)
+        def fn(x):
+            return reduce(ga, repeat(f, n), x)
+        return fn
+    return go
+# MAIN ---
+if __name__ == '__main__':
+    main()</lang>
+{{Out}}
+<pre>1500188 wakenings over 1000000 experiments.
+Sleeping Beauty should estimate credence
+at around 0.333</pre>
 =={{header|Raku}}==