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semantics.py
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semantics.py
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from __future__ import print_function
from abc import ABCMeta, abstractmethod
class Function:
__metaclass__ = ABCMeta
"""Abstract base class for state transition functions"""
@abstractmethod
def do_transition(self,state):
pass
def evaluate(self,state,verbose):
s,f = self.do_transition(state)
if verbose:
print("\n=>*"+str(f)+str(s))
while f!=None:
s,f = f.do_transition(s)
if verbose:
print("\n=>*"+str(f)+str(s))
return s
class Identity(Function):
"""
The Identity function that does not change the state
"""
def __init__(self):
super(Identity,self).__init__()
def do_transition(self,state):
return state.get_copy(),None
def __str__(self):
return "id"
class Undef(Function):
"""
The function that is always undefined (bottom)
"""
def __init__(self):
super(Undef,self).__init__()
def do_transition(self,state):
return state.null_state(),None
def __str__(self):
return '_'
class Update(Function):
"""
The function that change the state updating the value of a variable
"""
def __init__(self,varname,expr):
super(Update,self).__init__()
self.__v = varname
self.__e = expr
def do_transition(self,state):
val = self.__e.evaluate(state)
return state.update(self.__v,val),None
def __str__(self):
return "\s.s["+self.__v+"/A["+str(self.__e)+"]s]"
class Composition(Function):
"""
The composition of two state transition functions
"""
def __init__(self,first_function,second_function):
super(Composition,self).__init__()
self.__f1 = first_function
self.__f2 = second_function
def do_transition(self,state):
s1 = self.__f1.evaluate(state,False)
return s1,self.__f2#self.__f2.evaluate(s1,verbose)
def __str__(self):
return '('+str(self.__f2)+') o ('+str(self.__f1)+')'
class Cond(Function):
"""
\s.cond(b,s1,s2) = | s1 if B[b]s == tt
| s2 otherwise
"""
def __init__(self,bexp,S1,S2):
super(Cond,self).__init__()
self.__b = bexp
self.__s1 = S1
self.__s2 = S2
def do_transition(self,state):
condition = self.__b.evaluate(state)
if condition == True:
return state,self.__s1#self.__s1.evaluate(state,verbose)
if condition == False:
return state,self.__s2#self.__s2.evaluate(state,verbose)
return state.null_state(),None
def __str__(self):
return 'cond(B['+str(self.__b)+'],'+str(self.__s1)+','+str(self.__s2)+')'
class FixF(Function):
"""
Fix point of F g = cond(b,g o Sds[S],id)
"""
def __init__(self,condition,body):
super(FixF,self).__init__()
self.__b = condition
self.__s = body
def do_transition(self,state):
i = 10
s = Undef().evaluate(state,False)
while s.is_undef():
print("[ evaluating F^"+str(i)+" _ ] ...", end='\r')
f = self.__Fn_bottom(i)
s = f.evaluate(state,False)
i *= 10
return s,None
def __Fn_bottom(self,n):
k = 0
fn = Undef()
while k<n:
fn = Cond(
self.__b,
Composition(
self.__s,
fn
),
Identity()
)
k += 1
return fn
def __str__(self):
return 'FIX(\\g.cond(\n\tB['+str(self.__b)+'],\n\tg o ('+str(self.__s)+'),\n\tid\n\t))'