Parser-for-Perl-like

Simple-Perl-Like Language

Language definition

Lexical Analyser

• The syntax definitions of this Perl-like language are given below using Extended Backus–Naur form (EBNF) notations:

Usage	Notation
a character x	x
an escaped character	\x
M followed by N	MN
zero or more occurrences of M	M*
one or more occurrences of M	M+
zero or one occurrence of M	M?
definition	=
termination	;
alternation	|
optional	[ ... ]
repetition	{ ... }
grouping	( ... )
terminal string	' ... '
exception	-

• Identifiers (IDENT)

  • IDENT := [ Letter _ ] {( Letter | Digit | _ )}
  • Letter := [ a-z A-Z ]
  • Digit := [0-9]

• The variables are either numeric or string scalar variables. Numeric variables start by "$" while a string variables start by "@". Both are followed by an IDENT.

  • NIDENT := $ IDENT
  • SIDENT := @ IDENT

• Integer constants (ICONST)

  • ICONST := [0-9]+

• Real constants (RCONST)

  • RCONST := ([0-9]+).([0-9]*)

• String constants (SCONST)

  • SCONST := '[anything]+'

• Reserved words: writeln, if, and else

  • Tokens, respectively: WRITELN, IF, ELSE

• Terminals: semicolon, comma, left parenthesis, right parenthesis, left braces, and right braces

  • Tokens, respectively: SEMICOL, COMMA, LPAREN, RPAREN, LBRACES, and RBRACES

• Comment is defined by anything following “#” to the end of line and does not have a token

• Operators: +, -, *, /, ^, =, ==, >, <, . (dot), ** (repeat), -eq (string equality), -lt (string less than), and -gt (string greater than)

  • Tokens, respectively: PLUS, MINUS, MULT, DIV, EXPONENT, ASSOP, NEQ, NGTHAN, NLTHAN, CAT, SREPEAT, SEQ, SLTHAN, and SGTHAN

• Error (ERR)

• End of file (DONE)

Recursive-Desecent Parser

• Definition (using recursion):

1. Prog ::= StmtList
2. StmtList ::= Stmt ;{ Stmt; }
3. Stmt ::= AssignStme | WriteLnStmt | IfStmt
4. WriteLnStmt ::= writeln (ExprList)
5. IfStmt ::= if (Expr) ‘{‘ StmtList ‘}’ [ else ‘{‘ StmtList ‘}’ ]
6. AssignStmt ::= Var = Expr
7. Var ::= NIDENT | SIDENT
8. ExprList ::= Expr { , Expr }
9. Expr ::= RelExpr [(-eq|==) RelExpr ]
10. RelExpr ::= AddExpr [ ( -lt | -gt | < | > ) AddExpr ]
11. AddExpr :: MultExpr { ( + | - | .) MultExpr }
12. MultExpr ::= ExponExpr { ( * | / | **) ExponExpr }
13. ExponExpr ::= UnaryExpr { ^ UnaryExpr }
14. UnaryExpr ::= [( - | + )] PrimaryExpr
15. Primary ::= IDENT | SIDENT | NIDENT | ICONST | RCONST | SCONST | (Expr)

• Table of Operators Precedence Levels:

Precedence	Operator	Description	Associativity
1	Unary + , -	Unary plus and minus	Right to Left
2	^	Exponent	Right to Left
3	*, /, **	Multiplication, Division, and String repetition	Left to Right
4	+, -, . (Dot)	Addition, Subtraction, and String concatenation	Left to Right
5	<, >, -gt, -lt	- Numeric Relational - String Relational	no cascading
6	==, -eq	- Numeric Equality - String Equality	no cascading

Interpreter

• Implement Value class member functions and overloaded operators from val.h

• The interpreter provides:

  • Perform the syntax analysis of the input source code, statement by statement, then execute the statement if there is no error.
  • Build the information of the variables types in the symbol table for all the given defined variables.
  • Next, evaluate the expressions and determine the corresponding values and types.

How its built:

• Coding language: C++
• Libraries/Frameworks: string, queue, map, iomanip, stdexcept, cmath, sstream, and iostream

How to run:

• Clone this repo to your local IDE (VSCode/CLion).
• Run prog3.cpp by command line (including the testcase file name).