first stub of relational algebra to python converter

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@15 014f5005-505e-4b48-8d0a-63407b615a7c

parser.py

@@ -0,0 +1,60 @@
+# coding=UTF-8
+# Relation
+# Copyright (C) 2008  Salvo "LtWorf" Tomaselli
+# 
+# Relation is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+# 
+# author Salvo "LtWorf" Tomaselli <tiposchi@tiscali.it>
+
+def parse(expr):
+	'''This function parses a relational algebra expression, converting it into python, 
+	executable by eval function to get the result of the expression.'''
+	
+	#Selection σage > 25 Λ rank = weight(A)
+	#Projection π a,b(A)
+	#Rename ρid➡i,name➡n(A)
+	#A ᑌ B
+	#A ᐅᐊ B
+	#A ᑎ B
+
+	result=""
+	symbols={}
+	symbols["*"]=".product(%s)"
+	symbols["-"]=".difference(%s)"
+	symbols["ᑌ"]=".union(%s)"
+	symbols["ᑎ"]=".intersection(%s)"
+	symbols["ᐅᐊ"]=".join(%s)"
+	symbols["ᐅᐊLEFT"]=".outer_left(%s)"
+	symbols["ᐅᐊRIGHT"]=".outer_right(%s)"
+	symbols["ᐅᐊFULL"]=".outer(%s)"
+	
+	tokens=expr.split(" ")
+	
+	i=0;
+	tk_l=len(tokens)
+	while i<tk_l:
+		if tokens[i] not in symbols:
+			result+=tokens[i]
+		else:
+			
+			result+=symbols[tokens[i]] % (tokens[i+1])
+			i+=1
+		i+=1
+	return result
+		
+if __name__=="__main__":
+	while True:
+		e=raw_input("Expression: ")
+		print parse(e)
+