CS 280
Fall 2020
Programming Assignment 1
Fe
uary 22, 2021
Due Date: Wednesday, March 10, 2021, 23:59
Total Points: 20
In this programming assignment, you will be building a lexical analyzer for small programming
language and a program to test it. This assignment will be followed by two other assignments to
uild a parser and interpreter to the same language. Although, we are not concerned about the
syntax definitions of the language in this assignment, we intend to introduce it ahead of
Programming Assignment 2 in order to show the language reserved words, constants, and
operators. The syntax definitions of a Fortran-Like small programming language are given below
using EBNF notations. The details of the meanings (i.e. semantics) of the language constructs will
e given later on.
Prog = PROGRAM IDENT {Decl} {Stmt} END PROGRAM IDENT
Decl = Type : VarList
Type = INTEGER | REAL |CHAR
VarList = Var {,Var}
Stmt = AssigStmt | IfStmt | PrintStmt |ReadStmt
PrintStmt := PRINT , ExprList
IfStmt = IF (LogicExpr) THEN {Stmt} END IF
AssignStmt = Var = Expr
ReadStmt = READ , VarList
ExprList = Expr {, Expr}
Expr = Term {(+|-) Term}
Term = SFactor {(*|/) SFactor}
SFactor = Sign Factor | Factor
LogicExpr = Expr (== | <) Expr
Var = IDENT
Sign = + | -
Factor = IDENT | ICONST | RCONST | SCONST | (Expr)
Based on the language definitions, the lexical rules of the language and the assigned tokens to
terminals are as follows:
1. The language has identifiers, refe
ed to by ident terminal, which are defined to be a letter
followed by zero or more letters or digit. It is defined as:
ident := Letter {(Letter|Digit)}
Letter := [a-z A-Z]
Digit := [0-9]
The token for an identifier is IDENT.
2. Integer constants, refe
ed to by iconst terminal, are defined as one or more digits. It is defined
as:
iconst := [0-9]+
The token for an integer constant is ICONST.
3. Real constants, refe
ed to by rconst terminal, are defined as zero or more digits followed by a
decimal point (dot) and one or more digits. It is defined as:
Rconst := ([0-9]*)\.([0-9]+)
The token for a real constant is RCONST. For example, real number constants such as 12.0
and .2 are accepted, but 2. is not.
4. String literals, refe
ed to by sconst terminal, are defined as a sequence of characters delimited
y single or double quotes, that should all appear on the same line. The assigned token for a
string constant is SCONST. For example, “Hello to CS 280.” Or ‘Hello to CS
280.’ are string literals. There are no escape characters. However, a string delimited by single
quotes can have double quotes character as one of the characters of the string, and similarly a
string delimited by double quotes characters can have a single quote as one of the characters
of the string. For example, “welcome to smith’s home” or ‘welcome to
“smith” home’ are acceptable strings.
5. The reserved words of the language are: program, end, print, read, if, then, integer, real, char.
These reserved words have the following tokens, respectively: PROGRAM, END, PRINT,
READ, IF, THEN, INTEGER, REAL, and CHAR.
6. The operators of the language are: +, -, *, /,
, =, (, ), ==, <. These operators are for add,
su
act, multiply, divide, concatenate, assignment, left parenthesis, right parenthesis, equality,
and less than operations. They have the following tokens, respectively: PLUS, MINUS,
MULT, DIV, CONCAT, ASSOP, LPAREN, RPAREN, EQUAL, LTHAN.
7. The colon and comma characters are terminals with the following tokens: COLON, COMA.
8. A comment is defined by all the characters following the exclamation mark “!” to the end of
the line. A comment does not overlap one line. A recognized comment is ignored and does not
have a token.
9. White spaces are skipped. However, white spaces between tokens are used to improve
eadability and can be used as a one way to delimit tokens.
10. An e
or will be denoted by the ERR token.
11. End of file will be denoted by the DONE token.
Lexical Analyzer Requirements:
You will write a lexical analyzer function, called getNextToken, and a driver program for
testing it. The getNextToken function must have the following signature:
LexItem getNextToken (istream& in, int& linenumber);
The first argument to getNextToken is a reference to an istream object that the function should
ead from. The second argument to getNextToken is a reference to an integer that contains the
cu
ent line number. getNextToken should update this integer every time it reads a newline
from the input stream. getNextToken returns a LexItem object. A LexItem is a class that
contains a token, a string for the lexeme, and the line number as data members.
A header file, lex.h, is provided for you. It contains a definition of the LexItem class, and a
definition of an enumerated type of token symbols, called Token. You MUST use the header file
that is provided. You may NOT change it.
Note that the getNextToken function performs the following:
1. Any e
or detected by the lexical analyzer should result in a LexItem object to be returned
with the ERR token, and the lexeme value equal to the string recognized when the e
or
was detected.
2. Note also that both ERR and DONE are unrecoverable. Once the getNextToken
function returns a LexItem object for either of these tokens, you shouldn’t call
getNextToken again.
3. Tokens may be separated by spaces, but in most cases are not required to be. For example,
the input characters “3+7” and the input characters “ XXXXXXXXXX” will both result in the
sequence of tokens ICONST PLUS ICONST. Similarly, The input characters
“Hello” “World”, and the input characters “Hello””World”
will both result in the token sequence SCONST SCONST.
Testing Program Requirements:
It is recommended to implement the lexical analyzer in one source file, and the main test
program in another source file. The testing program is a main() function that takes several
command line flags. The notations for each input flag are as follows:
● -v (optional): if present, every token is printed when it is seen followed by its
lexeme between parentheses.
● -iconsts (optional): if present, prints out all the unique integer constants in numeric
order.
● -rconsts (optional): if present, prints out all the unique real constants in numeric
order.
● -sconsts (optional): if present, prints out all the unique string constants in
alphabetical order
● -ids (optional): if present, prints out all of the unique identifiers in alphabetical
order.
● filename argument must be passed to main function. Your program should open the
file and read from that filename.
Note, your testing program should apply the following rules:
1. The flag arguments (arguments that begin with a dash) may appear in any order, and may
appear multiple times. Only the last one is considered.
2. There can be at most one file name specified on the command line. If more than one filename
is provided, the program should print on a new line the message “ONLY ONE FILE NAME
ALLOWED” and it should stop running. If no file name is provided, the program should
print on a new line the message “NO SPECIFIED INPUT FILE NAME FOUND”, and
should stop running.
3. No other flags are permitted. If an unrecognized flag is present, the program should print on
a new line the message “UNRECOGNIZED FLAG {arg}”, where {arg} is whatever flag
was given, and it should stop running.
4. If the program cannot open a filename that is given, the program should print on a new line
the message “CANNOT OPEN THE FILE {arg}”, where {arg} is the filename given, and it
should stop running.
5. If getNextToken function returns ERR, the program should print “E
or in line N
({lexeme})”, where N is the line number of the token in the input file and lexeme is its
co
esponding lexeme, and then it should stop running. For example, a file that contains an
invalid real constant, as 15., in line 1 of the file, the program should print the message:
E
or in line 1 (15)
6. The program should repeatedly call getNextToken until it returns DONE or ERR. If it
eturns DONE, the program prints summary information, then handles the flags -sconsts, -
iconsts, rconsts and -ids, in that order.
The summary information are as follows:
Lines: L
Tokens: N
Where L is the number of input lines and N is the number of tokens (not counting DONE).
If L is zero, no further lines are printed.
7. If the -v option is present, the program should print each token as it is read and recognized,
one token per line. The output format for the token is the token name in all capital letters (for
example, the token LPAREN should be printed out as the string LPAREN. In the case of the
tokens IDENT, ICONST, RCONST, and SCONST, the token name should be followed by a
space and the lexeme in parentheses. For example, if the identifier “circle” and a string literal
"The center of the circle through these points is" are recognized, the -v output for them would
e:
IDENT (circle)
SCONST (The center of the circle through these points is)
8. The -sconsts option should cause the program to print the label STRINGS: on a line by itself,
followed by every unique string constant found, one string per line without double quotes, in
alphabetical order. If there are no SCONSTs in the input, then nothing is printed.
9. The -iconsts option should cause the program to print the label