grammar.txt

 program ::= extern_list decl_list 
           | decl_list
  extern_list ::= extern_list extern
               |  extern
  extern ::= "extern" type_spec IDENT "(" params ")" ";"
  decl_list ::= decl_list decl
             |  decl
  decl ::= var_decl 
        |  fun_decl
  var_decl ::= var_type IDENT ";" 
  type_spec ::= "void"
             |  var_type           
  var_type  ::= "int" |  "float" |  "bool"
  fun_decl ::= type_spec IDENT "(" params ")" block
  params ::= param_list  
          |  "void" | epsilon
  param_list ::= param_list "," param 
              |  param
  param ::= var_type IDENT
  block ::= "{" local_decls stmt_list "}"
  local_decls ::= local_decls local_decl
               |  epsilon
  local_decl ::= var_type IDENT ";"
  stmt_list ::= stmt_list stmt 
             |  epsilon
  stmt ::= expr_stmt 
        |  block 
        |  if_stmt 
        |  while_stmt 
        |  return_stmt
  expr_stmt ::= expr ";" 
             |  ";"
  while_stmt ::= "while" "(" expr ")" stmt 
  if_stmt ::= "if" "(" expr ")" block else_stmt
  else_stmt  ::= "else" block
              |  epsilon
  return_stmt ::= "return" ";" 
               |  "return" expr ";"               
  # operators in order of increasing precedence      
  expr ::= IDENT "=" expr
        | rval
  rval ::= rval "||" rval                                              
        | rval "&&" rval                                             
        | rval "==" rval | rval "!=" rval                            
        | rval "<=" rval | rval "<" rval | rval ">=" rval | rval ">" rval
        | rval "+" rval  | rval "-" rval
        | rval "*" rval  | rval "/" rval  | rval "%" rval
        | "-" rval | "!" rval
        | "(" expr ")"
        | IDENT | IDENT "(" args ")" 
        | INT_LIT | FLOAT_LIT | BOOL_LIT        
  args ::= arg_list 
        |  epsilon
  arg_list ::= arg_list "," expr
            |  expr