Name : Atusa Fattahi

Project name :
Interpreter for web scripting language

Directory :
~/proj/demsys/com3360/f97/atoosa/fproject

Credits :
SRC report 148 by Luca Cardelli and Rown Davies
http://www.research.digital.com/src/publications

Class dictionary :
(@ import java.util.* ;                                                 
   import java.net.*;                                                  
   import java.io.*;                                                    
   import java.lang.*;                                                  
  @)                                                                    
                                                                                
                          
// *implements* Runnable is needed because the run method of this class 
//is activated by a thread                                              
                                                                        
S = <service> Service *implements* Runnable.                            
                                                                        
Service : Basic_Service | Repetition | Time_Limit | Sequential_Execution
               | Concurrent_Execution .
                                                                        
Basic_Service = "url" "(" <address> Address ")".    

Repetition = "repeat" "(" <repeat>S ")".

Time_Limit = "timeout" "(" <time>Time "," <on>Block ")" .
                    
// first and second have been inserted to make the cd LL(1)             

                                                                        
Sequential_Execution = "first" <first> S "?" "second" <second> S .      

// Main and Thread have been inserted to make the cd LL(1)             
                                                                       
Concurrent_Execution = "main"<main>S "|" "thread"<thread>S.

Address = <string>String.                                                

Time = <l>long.                                                        
                                                                       
Block : S | Stall.                                                     
                                                                       
Stall = "stall".                                                       

Main=.


Basic service
url(String)
this service fetches the resource associated with the URL indicated by 
the string. The result returned is the content fetched . The service 
fails if the fetch fails.

Sequential Execution
first S1 ?  second S2
the ? combinator allows a secondary service to be done in the case that 
the primary service fails for some reason. Thus the service S1 ? S2 acts 
like the service S1,except that if S1 fails then it acts like the service S2

Concurrent Execution
main S1 |  thread S2
The "|" combinator allows two services to be executed concurrently. The 
service S1 | S2 start both services at the same time.

Time Limit
timeout( t , s)
The time out combinator allows a time limit to be placed on a service. 
This service acts like S except that it fails after t amount of time  if  
S has not completed yet.


Repetition
repeat(S)
The repeat combinator provides a way to repeatedly invoke a service until 
it succeeds.The service repeat( S ) acts like S except that if S fails, 
repeat(s) starts again.


there were two other services
one was Gateways
       index(String, String)
       gateway get(String, id[1]=String[1]...id[n]=String[n])
       gateway post(String, id[1]=String[1]...id[n]=String[n])
each of which is similar to the service url(string), except that  it 
should be associated  with a CGI gateway having the corresponding type.

as  Java language has four different kinds of URL constructors this 
service  can easily be implemented by using the other constructors 
available 


URL(String) 
Creates a URL object from the String representation. 
URL(String, String, int, String) 
Creates a URL object from the specified protocol, host, port number, and 
file. 
URL(String, String, String) 
Creates an absolute URL from the specified protocol name, host name, and 
file name. 
URL(URL, String) 
Creates a URL by parsing the specification spec within a specified 
context.

this feature can be implemented exactly the way a url(String) was 
implemented and using the other three constructors instead of the first one.

the other service is Rate Limit
limit(t,r,S)
this service acts like Time Limit service including another limitation on 
rate limit, in case the rate of transmission drops below r the service 
should fail.The way this service should be implemented is exactly  like 
time limit with another limitation .To find out  the rate of transmission 
is something that should be figured out in Java.

Growth plan :
I didn't keep my growth phases but  this is what I did :
I implemented a read function in plain Java  that reads the content of a url
Then I designed a simple cd with only a  Basic_Service  class and started 
writing code for it in the behavior file . When this part was compiled 
and tested I added another service to it and started writing code for 
this new class . If I call the program with only the Basic_Service class 
the Basic Program (BP)  and call the program which was going to have all 
the services at end the Main Program (MP)
I added and implemented each service to BP and after it was compiled I 
added it to MP and tested it again . Some times I might need to make some 
changes to the program which was added to MP because the cd is very 
recursive . the final MP is the program that I turned in as my project .

The output of my project is now an html file with some messages . It 
would be nice to write another interpreter that interprets  an html file .
If I had more time I would have liked to add the two other services that 
have been left out , as I have said before the way they should be 
implemented is not  different just more time was needed .
I tried to implement the ones that were different first and do more 
adaptive programming  than Java programming .

The input of this program reads only one service .To make it read a list of 
services this command should be added to the cd file 
List(K) ~ { K }.
and change the first line to : S = List(Service).
I don't think there would be any problems if this change is made but as I 
haven't test it with any inputs I thought I better not.

I didn't change the Java code any where but as I am using Threads and at any 
time there might be any number of threads runnung at the same time and 
writing to the output I had to know which methods were using println to include
them in the mutex and selfex in the cool file, for this I needed to check the
java files.

My final program is in ~/proj/demsys/com3360-f97/fproject
in this directory I included
READ_ME
program.beh
program.cd
program.cool
program.input
mainoutput
input/ input1 ... input7
output/output1 ... output7

the easiest way to write an input for this program is to draw a tree 
according to the cd file and then make it readable as an input.