Add regex_to_nfa.py

regex_to_nfa.py

@@ -0,0 +1,105 @@
+from regex import Literal, Concatenation, Alternation, Star, lit, concat, bar, star
+from nfa import NFA, prettyprint
+
+def to_nfa(regex):
+	def new_state():
+		nonlocal state_name_counter, transitions
+
+		state_name = state_name_counter
+		state_name_counter += 1
+
+		transitions[state_name] = {}
+
+		return state_name
+
+	def worker(node):
+		nonlocal transitions
+
+		if type(node) == Literal:
+			#            text
+			# (start) ---------> (end)
+			start_state = new_state()
+			end_state = new_state()
+
+			transitions[start_state][end_state] = lit(node.text)
+
+			return (start_state, end_state)
+
+		elif type(node) == Concatenation:
+			# (start) → […] → […] → […]
+			start_state = new_state()
+
+			prev_state = start_state
+			for element in node.elements:
+				inner_start, inner_end = worker(element)
+
+				# (prev) → (inner_start) → […]
+				transitions[prev_state][inner_start] = lit('')
+
+				# Link next element straight to the inner end
+				# state
+				prev_state = inner_end
+
+			return (start_state, prev_state)
+
+		elif type(node) == Alternation:
+			#           +-> […] --+
+			#           |         |
+			# (start) --+-> […] --+-> (end)
+			#           |         |
+			#           +-> […] --+
+			start_state = new_state()
+			end_state = new_state()
+
+			for element in node.elements:
+				inner_start, inner_end = worker(element)
+
+				# (start) → (inner_start) → […]
+				transitions[start_state][inner_start] = lit('')
+
+				# […] → (inner_end) → (end)
+				transitions[inner_end][end_state] = lit('')
+
+			return (start_state, end_state)
+
+		elif type(node) == Star:
+			#  +- […] <-+
+			#  |        |
+			#  v        |
+			# (start) --+--> (end)
+			start_state = new_state()
+			end_state = new_state()
+
+			inner_start, inner_end = worker(node.element)
+
+			# (start) → (inner_start) → […]
+			transitions[start_state][inner_start] = lit('')
+
+			# […] → (inner_end) → (start)
+			transitions[inner_end][start_state] = lit('')
+
+			# (start) → (end)
+			transitions[start_state][end_state] = lit('')
+
+			return (start_state, end_state)
+
+		else:
+			raise ValueError('node has to be Literal, Concatenation, Alternation, or Star')
+
+	state_name_counter = 0
+	transitions = {}
+
+	start_state, end_state = worker(regex)
+
+	return NFA(start_state, [end_state], transitions)
+
+def main():
+	regex = concat(lit('x'), star(bar(lit('a'), lit('b'))), lit('y'))
+	print(regex)
+
+	nfa = to_nfa(regex)
+
+	prettyprint(nfa)
+
+if __name__ == '__main__':
+	main()