(* Puff- an interpreted language *)
(* See the copyright notice at the end of this file. *)

(*
  Syntax
    EXPR = EXPR9
    
    EXPRb = EXPRa (";" EXPRa)*
    
    EXPRa = EXPR9 "|" EXPR9
    
    EXPR9 = EXPR8 ("," EXPR8)*
    
    EXPR8 = EXPR7 ("->" EXPR7)? | ID ":" EXPR7
    
    EXPR7 = ("+" | "-" | ".")? EXPR6 ("or" EXPR6)?
    
    EXPR6 = EXPR5 ("and" EXPR5)?
    
    EXPR5 = ("not")* EXPR4
    
    EXPR4 = EXPR3 (("="|"<"|">"|">="|"<="|"<>") EXPR3)?
    
    EXPR3 = ("+"|"-"|"&")? EXPR2 (("+"|"-"|"&") EXPR2)*
    
    EXPR2 = ("*"|"/")? EXPR1 (("*"|"/") EXPR1)*
    
    EXPR1 = EXPR0
    
    EXPR0 = "(" EXPR ")" | CONST | CALL | COND | LET
    
    CONST = '"'STRING'"' | DIGIT+('"'CHARS'"')?
    
    CALL = EXPR (EXPR)*
    
    ID = LETTER(("_")?(DIGIT|LETTER))*
    
    COND = ("select" EXPR)? "if" ((EXPR|"else") "->" EXPR)* "fi"
    
    LET = "let" ID ("(" ID ("," ID)* (",")?)? "=" EXPR "end"
    
  Comments start from "#" and extend to end-of-line
    
*)

TYPE
  Valu = PuffValu.T;
  
  Sign = [-1..+1];
  
  Source = REF RECORD
      name: TEXT;
      rd: Rd.T;
      lin: CARDINAL;
      col: CARDINAL;
      rest: Source;
    END;

  Context = REF RECORD
      arg: Valu;
      img: Valu;
      rest: Context;
    END;
    
    
PROCEDURE ParseExprb() =
  BEGIN
    LOOP
      v := ParseExpra();
      SkipBlanks();
      IF NOT NextTokenIs(";") THEN RETURN v END;
      IF NoMoreExpr() THEN RETURN NIL END
    END
  END ParseExprb

    
PROCEDURE Equal(a, b: Valu): BOOLEAN =
  BEGIN
    TYPECASE a OF 
      TEXT(a) -> 
        TYPECASE b OF TEXT(b) -> RETURN Text.Compare(a,b) ELSE RETURN FALSE END;
      Context(a) ->
      Pair(a) ->
      List(a) ->
    END~
  END~
  
PROCEDURE Lookup(arg: Valu; ctx: REF Context) =
  BEGIN
    
  END~