cminus1.atg

一个Modula-2语言分析器

COMPILER CMinus
(* Simple CMinus grammar.  P.D. Terry, Rhodes University, 1995 *)

CHARACTERS
  eol        = CHR(13) .
  letter     = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" .
  digit      = "0123456789" .
  noquote1   = ANY - "'" - eol .
  noquote2   = ANY - '"' - eol .

IGNORE CHR(9) .. CHR(13)
COMMENTS FROM "//" TO eol

TOKENS
  identifier = letter {letter | digit} .
  number     = digit { digit} .
  string     = '"' (noquote2 | '\"') { noquote2 | '\"' } '"' .
  char       = "'" ["\"] noquote1 "'" | "'\''" .

PRODUCTIONS

(* The main program can nest procedures, but procedures cannot nest procedures
   themselves.  This can be handled in a context free way by having a
   MainBlock and a ProcBlock non-terminal. *)

   CMinus             =  "void" identifier FormalParameters
                          MainBlock .

   MainBlock          =  "{"
                            { ConstDeclaration
                              | ProcDeclaration
                              | VarDeclarations }
                            { Statement }
                         "}" .

   ConstDeclaration   =  "const" identifier "=" number ";" .

   VarDeclarations    =  "int"
                            identifier [ UpperBound ]
                            { "," identifier [ UpperBound ] } ";"  .

   UpperBound         =  "[" ( number | identifier ) "]" .

   ProcDeclaration    =  ( "function" | "void" ) identifier FormalParameters
                           ( ProcBlock | ";" ) .

   FormalParameters   =  "(" [ FormalPar { "," FormalPar } ] ")" .

   FormalPar          =  identifier [ "[" "]" ] .

   ProcBlock          =  "{"
                           { ConstDeclaration | VarDeclarations }
                           { Statement }
                         "}" .

(* The rule for semicolons is very different from Pascal/Modula, where they
   are separators. *)

   CompoundStatement  =  "{" { Statement } "}" .

   Statement          =  CompoundStatement | AssignmentOrCall
                           | IfStatement | WhileStatement | ForStatement
                           | LoopStatement | ExitStatement | WriteStatement
                           | ReadStatement | ReturnStatement | ";" .

   AssignmentOrCall   =  Designator
                         ( "=" Expression | ActualParameters | "++" | "--" ) ";" .

   Designator         =  identifier [ "[" Expression "]" ] .

   ActualParameters   =  "(" [ ActualPar { "," ActualPar } ] ")" .

   ActualPar          =  Expression .

   IfStatement        =  "if" "(" Expression ")" Statement
                         [ "else" Statement ] .

   WhileStatement     =  "while" "(" Expression ")" Statement .

   ForStatement       =  "for" "(" [ Initial ] ";" Expression ";" [ Final ] ")"
                         Statement .

   Initial            =  Designator "=" Expression .

   Final              =  Designator ( "++" | "--" ) .

   LoopStatement      =  "loop" Statement .

   ExitStatement      =  "exit" ";" .

   WriteStatement     =  "cout" "<<" Expression { "<<" Expression } ";" .

   ReadStatement      =  "cin" ">>" Designator { ">>" Designator } ";" .

   ReturnStatement    =  "return" [ Expression ] ";" .

   Expression         =  SimpleExpression [ RelOp SimpleExpression ] .

   SimpleExpression   =  [ Sign ] Term { AddOp Term } .
                          
   Term               =  Factor { MulOp Factor } .

   Factor             =  Designator [ ActualParameters ]
                           | number | char | string
                           | "(" Expression ")"
                           | "!" Factor .

   Sign               =  "+" | "-" .

   AddOp              =  "+" | "-" | "||" .

   MulOp              =  "*" | "/" | "%" | "&&" .

   RelOp              =  "==" | "!=" | "<" | "<=" | ">" | ">=" .

END CMinus.