cs Homework 2 Solution

    • Introduction

In this homework you will write a context free grammar and implement a simple parser for MailScript language for which you designed a scanner in the previous homework. The language that will be generated by your grammar and other requirements of the homework are explained below.


    • MailScript Language

The grammar you will design needs to generate the MailScript language as described below. Here is an example program written in this language. This is to give you an idea how a MailScript program looks like.

set Message ("Welcome to CS305.")

Mail from nermin@mail.com:

schedule @ [27/10/2021, 07:48]:

send [Message] to [("Kerem", kerem@mail.com.tr)] end schedule

set Message ("Our project is due tomorrow.")

send [Message] to [("Mine", mine@mail.com), (selim@mail.com)]


end Mail

Mail from nermin@sabanciuniv.edu:

end Mail



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Mail from serkan@sabanciuniv.edu:

set UserName ("There is a meeting at 3pm.")

schedule @ [02/10/2021, 16:00]:

send [MorningMessage] to [(ali@mail.com), ("John Doe", emre@mail.com), (UserName, ali@mail.com)]

send ["How are you?"] to [("Omer", omer@mail.com)]

end schedule

end Mail




Note that the set of statements given above does not have to make sense. It may even have errors as a MailScript program. For example: There can be a usage of an undeclared variable or the recipient list can contain the same e-mail more than once.

We have some examples of such errors in the example MailScript program given above. However, in this homework we will not aim to detect such errors. In this homework, we will aim to implement a parser for the basic syntax rules of the MailScript language that are given in detail below.

    1. A MailScript program consists of a sequence of components, where each com-ponent is either a mail block or a set statement. Any number of mail blocks and set statements can be given in any order in a MailScript program. An empty program is also considered as a MailScript program.

    2. A mail block starts with the "Mail from" keyword, followed by the e-mail ad-dress that the user wants to send an e-mail from, followed by a colon symbol. Each mail block ends with the keyword "end Mail". Inside of a mail block can be empty or contain a statement list. A statement list is de ned as one or more statements given after one another.

    3. Each statement in the MailScript language can be a \set", \send" or \schedule" statement.

        (i) A set statement is used to assign a variable a value. It starts with the key-word \set" followed by the name of the variable, followed by a left parenthe-sis, followed by a string, followed by a right parenthesis. Please note that a set statement can exist both in and out of mail blocks.

set Notification ("Don t forget to set the alarm.")

Mail from melis@sumail.com:

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set Content ("Meeting at 5pm.")

end Mail

set Notification ("Set the alarm for 9am.")

    (ii) A send statement is used to send an e-mail. It starts with the keyword \send", followed by a left bracket, followed by either a variable name or a string, followed by a right bracket, followed by the keyword \to", followed by a recipient list. Some examples are given below:

set Message ("How are you?")

send ["Good morning!"] to [(user1@mail.com)] send [Message] to [(user2@mail.com)]

    (iii) A schedule statement is used to schedule a time for one or more e-mails to be sent. It also is formed like a block. Each schedule block starts with the keyword \schedule", followed by the @ symbol, followed by a left bracket, followed by a date and a time object separated by a comma, followed by a right bracket, nally followed by a colon symbol. Each schedule block ends with the keyword \end Schedule". Inside of a schedule block can ONLY contain a list of one or more send statements, it cannot be empty. An example is given below:

schedule @ [18/10/2021, 12:00]:

send ["HW is assigned!"] to [(example@mail.com)] send ["Please check the gradebook."] to [(example@mail.com), (admin123@mail.com)]

end schedule

    4. Please note that the schedule and send statements can only appear in mail blocks. On the other hand, a set statement can exist in or out of a mail block.

    5. A recipient object can be given in two forms. The rst form starts with a left parenthesis, followed by an e-mail address, followed by a right parenthesis. The second form starts with a left parenthesis, followed by either a variable name or a string, followed by a comma, followed by an e-mail address, followed by a right parenthesis. Some examples are given below:

(user_475@some-company.co.uk)

("Mehmet", user_475@some-company.co.uk)

    6. A recipient list starts with a left bracket, followed by a comma separated list of recipient objects (or a single recipient object), followed by a right bracket. It cannot be empty. An example is given below:

[("Ayse", ayse3@thismail.com), ("Unknown User", user8564@mail.com), (seyma@example.de)]




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    • Terminal Symbols

Although you can implement your own ex scanner, we provide a ex scanner for this homework. The provided ex scanner implements the following tokens.

tMAIL: The scanner returns this token when it sees Mail in the input.


tENDMAIL: The scanner returns this token when it sees end Mail in the input.


tSCHEDULE: The scanner returns this token when it sees schedule in the input.


tENDSCH: The scanner returns this token when it sees end schedule in the input.


tSEND: The scanner returns this token when it sees send in the input.


tSET: The scanner returns this token when it sees set in the input.


tTO: The scanner returns this token when it sees to in the input.


tFROM: The scanner returns this token when it sees from in the input.


tAT: The scanner returns this token when it sees an @ in the input.


tCOMMA: The scanner returns this token when it sees a comma in the input.


tCOLON: The scanner returns this token when it sees a : in the input.


tLPR: The scanner returns this token when it sees a ( in the input.


tRPR: The scanner returns this token when it sees a ) in the input.


tLBR: The scanner returns this token when it sees [ in the input.


tRBR: The scanner returns this token when it sees ] in the input.


tIDENT: The scanner returns this token when it sees an identi er in the input.


tSTRING: The scanner returns this token when it sees a string in the input.



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tADDRESS: The scanner returns this token when it sees an e-mail address in the input.


tDATE: The scanner returns this token when it sees a date in the input.


tTIME: The scanner returns this token when it sees a time in the input.


Besides these tokens, it silently consumes any white space character. Any other char-acter which is not recognized as a lexeme of the tokens is returned to the parser.


    • Output

Your parser must print out OK and produce a new line, if the input is grammatically correct. Otherwise, your parser must print out ERROR and produce a new line.

In other words, the main part in your parser le must be as follows (and there should be no other part in your parser that produces and output):

int main ()

{

if (yyparse())

{

    • parse error printf("ERROR\n"); return 1;

}

else

{

    • successful parsing printf("OK\n"); return 0;

}

}


    • How to Submit

Submit your Bison le named as username-hw2.y, and ex le named as username-hw2.flx where username is your SU-Net username and do not zip your les. We will compile your les by using the following commands:

flex username-hw2.flx

bison -d username-hw2.y

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gcc -o username-hw2 lex.yy.c username-hw2.tab.c -lfl

So, make sure that these three commands are enough to produce the executable parser. If we assume that there is a text le named test17.ms, we will try out your parser by using the following command line:



username-hw2 < test17.ms

If the le test17 includes a grammatically correct MailScript program then your output should be OK otherwise, your output should be ERROR.


    • Notes

        ◦ Important: Name your les as you are told and don’t zip them. [-10 points otherwise]

        ◦ Important: Make sure you include the right le in your scanner and make sure you can compile your parser using the commands given in the section 5. If we are not able to compile your code with those commands your grade will be zero for this homework.

        ◦ Important: Since this homework is evaluated automatically make sure your output is exactly as it is supposed to be. (i.e. OK for grammatically correct and ERROR otherwise).

        ◦ No homework will be accepted if it is not submitted using SUCourse+.

        ◦ You may get help from our TA or from your friends. However, you must write your bison le by yourself.

        ◦ Start working on the homework immediately.

        ◦ No email submission will be accepted.

        ◦ If you develop your code or create your test les on your own computer (not on ow.sabanciuniv.edu), there can be incompatibilities once you transfer them to ow.sabanciuniv.edu. Since the grading will be done automatically on the ow.sabanciuniv.edu, we strongly encourage you to do your development on ow.sabanciuniv.edu, or at least test your code on ow.sabanciuniv.edu before submitting it. If you prefer not to test your implementation on ow.sabanciuniv.edu, this means you accept to take the risks of incompatibility. Even if you may have spent hours on the homework, you can easily get 0 due to such incompatibilities.

        ◦ LATE SUBMISSION POLICY:

Late submission is allowed subject to the following conditions:


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{ Your homework grade will be decided by multiplying what you get from the test cases by a \submission time factor (STF)".

{ If you submit on time (i.e. before the deadline), your STF is 1. So, you don’t lose anything.

{ If you submit late, you will lose 0.01 of your STF for every 5 mins of delay. { We will not accept any homework later than 500 mins after the deadline. { SUCourse+’s timestamp will be used for STF computation.

{ If you submit multiple times, the last submission time will be used.





















































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