tasks a-s

Task/Execute-a-Markov-algorithm/Python/execute-a-markov-algorithm.py

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+import re
+
+def extractreplacements(grammar):
+    return [ (matchobj.group('pat'), matchobj.group('repl'), bool(matchobj.group('term')))
+                for matchobj in re.finditer(syntaxre, grammar)
+                if matchobj.group('rule')]
+
+def replace(text, replacements):
+    while True:
+        for pat, repl, term in replacements:
+            if pat in text:
+                text = text.replace(pat, repl, 1)
+                if term:
+                    return text
+                break
+        else:
+            return text
+
+syntaxre = r"""(?mx)
+^(?:
+  (?: (?P<comment> \# .* ) ) |
+  (?: (?P<blank>   \s*  ) (?: \n | $ )  ) |
+  (?: (?P<rule>    (?P<pat> .+? ) \s+ -> \s+ (?P<term> \.)? (?P<repl> .+) ) )
+)$
+"""
+
+grammar1 = """\
+# This rules file is extracted from Wikipedia:
+# http://en.wikipedia.org/wiki/Markov_Algorithm
+A -> apple
+B -> bag
+S -> shop
+T -> the
+the shop -> my brother
+a never used -> .terminating rule
+"""
+
+grammar2 = '''\
+# Slightly modified from the rules on Wikipedia
+A -> apple
+B -> bag
+S -> .shop
+T -> the
+the shop -> my brother
+a never used -> .terminating rule
+'''
+
+grammar3 = '''\
+# BNF Syntax testing rules
+A -> apple
+WWWW -> with
+Bgage -> ->.*
+B -> bag
+->.* -> money
+W -> WW
+S -> .shop
+T -> the
+the shop -> my brother
+a never used -> .terminating rule
+'''
+
+grammar4 = '''\
+### Unary Multiplication Engine, for testing Markov Algorithm implementations
+### By Donal Fellows.
+# Unary addition engine
+_+1 -> _1+
+1+1 -> 11+
+# Pass for converting from the splitting of multiplication into ordinary
+# addition
+1! -> !1
+,! -> !+
+_! -> _
+# Unary multiplication by duplicating left side, right side times
+1*1 -> x,@y
+1x -> xX
+X, -> 1,1
+X1 -> 1X
+_x -> _X
+,x -> ,X
+y1 -> 1y
+y_ -> _
+# Next phase of applying
+1@1 -> x,@y
+1@_ -> @_
+,@_ -> !_
+++ -> +
+# Termination cleanup for addition
+_1 -> 1
+1+_ -> 1
+_+_ ->
+'''
+
+grammar5 = '''\
+# Turing machine: three-state busy beaver
+#
+# state A, symbol 0 => write 1, move right, new state B
+A0 -> 1B
+# state A, symbol 1 => write 1, move left, new state C
+0A1 -> C01
+1A1 -> C11
+# state B, symbol 0 => write 1, move left, new state A
+0B0 -> A01
+1B0 -> A11
+# state B, symbol 1 => write 1, move right, new state B
+B1 -> 1B
+# state C, symbol 0 => write 1, move left, new state B
+0C0 -> B01
+1C0 -> B11
+# state C, symbol 1 => write 1, move left, halt
+0C1 -> H01
+1C1 -> H11
+'''
+
+text1 = "I bought a B of As from T S."
+
+text2 = "I bought a B of As W my Bgage from T S."
+
+text3 = '_1111*11111_'
+
+text4 = '000000A000000'
+
+
+if __name__ == '__main__':
+    assert replace(text1, extractreplacements(grammar1)) \
+           == 'I bought a bag of apples from my brother.'
+    assert replace(text1, extractreplacements(grammar2)) \
+           == 'I bought a bag of apples from T shop.'
+    # Stretch goals
+    assert replace(text2, extractreplacements(grammar3)) \
+           == 'I bought a bag of apples with my money from T shop.'
+    assert replace(text3, extractreplacements(grammar4)) \
+           == '11111111111111111111'
+    assert replace(text4, extractreplacements(grammar5)) \
+           == '00011H1111000'