Recursive Descent Parser

Top down parser which checks if the input is part of the language or not.

Token

   Program --> Sequence State  
   Sequence --> (Statements)  
   Statements --> Statements Stmt | Stmt  
   Stmt --> NullStatement | Assignment | Conditional | Loop | Block  
   State -->  (Pairs)  
   Pairs --> Pairs Pair | Pair  
   Pair --> (Identifier Literal)  
   NullStatement --> (skip)  
   Assignment --> (assign Identifier Expression)  
   Conditional --> (conditional Expression Stmt Stmt)  
   Loop --> (loop Expression Stmt)  
   Block --> (block Statements)  
   Expression --> Identifier | Literal | (Operation Expression Expression)  
   Operation --> + | - | * | / | < | <= | > | >= | = | != | or | and  

Scanner

BNF grammar of Mini Language

   Program" --> "("Sequence State")"  
   Sequence --> "("Statements")"  
   Statements --> Statements  Stmt | e  
   Stmt --> "(" {NullStatement | Assignment | Conditional | Loop | Block}")"  
   State -->  "("Pairs")"  
   Pairs -->  Pairs Pair | e  
   Pair --> "("Identifier Literal")"  
   NullStatement --> "skip"  
   Assignment --> "assign" Identifier Expression  
   Conditional --> "conditional" Expression Stmt Stmt  
   Loop --> "loop" Expression Stmt  
   Block --> "block" Statements  
   Expression --> Identifier | Literal | "("Operation Expression Expression")"  
   Operation --> "+" |"-" | "*" | "/" | "<" | "<=" | ">" | ">=" | "=" | "!=" | "or" | "and"  

Note: Symbol e means Symbol e means epsilon. Treat Identifier and Literal as terminal symbols. Every symbol inside " and " is a terminal symbol. The rest are non terminals.

Parser

EBNF of Mini Language

   Program" --> "("Sequence State")"  
   Sequence --> "("Statements")"  
   Statements --> Stmt*  
   Stmt --> "(" {NullStatement | Assignment | Conditional | Loop | Block}")"  
   State -->  "("Pairs")"  
   Pairs -->  Pair*  
   Pair --> "("Identifier Literal")"  
   NullStatement --> "skip"  
   Assignment --> "assign" Identifier Expression  
   Conditional --> "conditional" Expression Stmt Stmt  
   Loop --> "loop" Expression Stmt  
   Block --> "block" Statements  
   Expression --> Identifier | Literal | "("Operation Expression Expression")"  
   Operation --> "+" |"-" | "*" | "/" | "<" | "<=" | ">" | ">=" | "=" | "!=" | "or" | "and"  

Note: Treat Identifier and Literal as terminal symbols. Every symbol inside " and " is a terminal symbol. The rest are non terminals.