Project Phase1: Scanning and Parsing using Lex and Yacc
1 AA Language
For this phase, you will use Lex tool for writing the scanner and Yacc tool for writing the parser for a programming language called AA.
Part 1: The Scanner and the Lexemes:
- Keywords: int, double, if, read, print, while,START,END.
- Operators:
- Arithmetic: + , - , * , /
- Logic: &&,||,!
- Relational: ==, <>, <, <=, >,>=
- Assignment: =
- Punctuation elements: (),,,{}
Precedence and associativity
The table below shows all AA operators from highest to lowest precedence, along with their associativity.
Table 1: precedence and associativity table
|
Operator
|
Description
|
Associativity
|
|
!
|
Unary Logical NOT
|
right to left
|
|
∗/
|
Multiplication/Division
|
left to right
|
|
+-
|
Addition/ Subtraction
|
left to right
|
|
<, <=, >,>=
|
Relational
|
left to right
|
|
=<>
|
Equality
|
left to right
|
|
&&
|
Logical AND
|
left to right
|
|
||
|
Logical OR
|
left to right
|
|
=
|
Assignment
|
right to left
|
Identifiers: should start with capital letter and can include small, capital letters, underscores, or digits.
- Comment: is sequence of any characters between double hash ##. ##
Literals: INT LITERAL e.g. 12345, STRING LITERAL e.g. "Hello"and DBL LITERAL e.g. 3.14.
Part 2: The Parser and the Grammar:
When YACC finds input that doesn't match the grammar, it automatically termi- nates with the message 'Syntax error'. You will need to implement an error routine (yyerror) that also prints out the line number before this termination, and a main method that read AA code from a file. Print an appropriate message in case of no syntax error. Build your parser using the grammar below:
Start→ Program START Statements END
Statements → Statements Statement| Statement
Statement→ Dec stmt | Assignment stmt | Print stmt | Read stmt
| Condition stmt | While stmt
Dec stmt→ Type ID |Type ID,IDList IDList → ID | ID,IDList
Type→ int | double
Assignment stmt→ID = Expression
Expression → exp == exp | exp <> exp | exp < exp | exp <= exp| exp >= exp | exp >= exp | exp
exp→ exp + exp | exp - exp| exp * exp | exp /exp | exp || exp | exp && exp | !exp | Factor
Factor→ ( exp )| INT LITERAL | DBL LITERALL | ID Print stmt→ print ( ID ) | print ( STRING LITERAL ) Read stmt→ ID = read ( )
Condition stmt→ if (Expression ) statements While stmt→ while ( Expression ) statements
Deliverable and rules
Write the Lex and Yacc file for AA language as described above. Once you built your parser, you should be able to parse AA programs. If you want to test your code, consider the following program.
Start
int X12 double ABC1 DDe =7
while ( QNn >0) ## this a Comment ##
{ RLk 9999 = ACc - 2
CCC = True
if( ACc == 5){ print (" Inside . IF. inside . Loop ") } } print (" Hello ")
End
This program should be compiled and have no errors. Note that this program does not cover all functionalities that could be tested based on the given specification. Test your code thoroughly. If the input program is in different syntax than the given grammar, your parser should report an error.
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