Non-local references

So far, whenever we needed to compute a variable, there  was  a binding for that  variable in the 'local' environment (the environment in which  we were evaluating the expression). But take this code:

 

def biz(a):

return a + b

 

>>> b = 6

 

 

We need to elaborate, slightly,  how it is that a variable v is computed in an environment E:

 

• We take if there is a binding for v in E; if so, we stop and return it.

 

• If not, we compute v in the parent environment of E. If E has no base, we create an error.

 

It is important to check that this method  will continue up an arbitrarily long chain of environ­ ments  and their parents until either a binding for v is found or there are no more environments to examine.

So, in our case, we will compute the expression a + b in environment E2. We start by calculating a and searching value 2 in E2. Then, we compute b and cannot search it in E2...but we don't panic! We take the parent pointer to E1 and  try again.  We search a binding for b in E1 and  get the value  6. So, the value  of a + b in E2 is 8.

 

Posted Date: 8/11/2012 2:43:21 AM | Location : United States

Ask an Expert

Related Discussions:- Non-local references, Assignment Help, Ask Question on Non-local references, Get Answer, Expert's Help, Non-local references Discussions

Write discussion on Non-local references
Your posts are moderated

Write your message here..

Related Questions

Analytical models, Analytical models Analytical tools  are very importa... Analytical models Analytical tools  are very important.  It may  be hard  to check  the  correctness of a machine by trying it in several possible  initial  conditions with  al

Foundation of programming, hi i want to make a assignmnt of foundation of p... hi i want to make a assignmnt of foundation of programming which include 4 task. I just want to know how much will be the price for that

Help, When investing money, an important concept to know is compound intere... When investing money, an important concept to know is compound interest. The equation FV = PV (1+rate)periods . This relates the following four quantities. The present value (

Euler method, python program of motion of a particle in viscus medium python program of motion of a particle in viscus medium

Normalize a vector, Normalize a vector Let's imagine we want  to norma... Normalize a vector Let's imagine we want  to normalize a vector  of three  variables;  that  is to compute a new  vector  of three values,  such that its size  is 1. Here is o

Basic-learning to program in python , Depending on your  previous programmi... Depending on your  previous programming background, we use different sides  through the available readings:   If you have never programmed before: you should start with a

Python implementation of a solver for the desert crossing, Assume you have ... Assume you have a truck which has to travel across a desert from the base camp at position 0 (left) to the target camp at position 4 (right). The intermediate positions 1,2, and 3

Otway rees protocol implementation, I need server, client and trusted side ... I need server, client and trusted side communicating and charging a service with that protocol (or needham shroeder)

Psuedocode, #ques Write the pseudocode (use a word processor please) and th... #ques Write the pseudocode (use a word processor please) and the Python 3.0 program for the following problem. A monkey is being fed some food. Read in the starting weight in lbs:o

Primitives, Primitives, Composition, Abstraction, and Patterns   We ... Primitives, Composition, Abstraction, and Patterns   We will  start  by thinking about  how  the  PCAP  framework applies to computer programs, in general. We may do that by