juno-machine/src/JunoValue.i3

 Copyright (C) 1992, Digital Equipment Corporation                         
 All rights reserved.                                                      
 See the file COPYRIGHT for a full description.                            
                                                                           
 Last modified on Thu Mar 28 14:48:21 PST 1996 by heydon                   
      modified on Tue Nov 29 14:25:33 PST 1994 by gnelson                  


INTERFACE JunoValue;

 A JunoValue.T represents a Juno value. A value in Juno is either nil, a
   real number, a text string, or a pair of values.


   This interface also defines the procedure Unparse to pretty-print a value
   to a Wr.T, and the procedure Equal to determine if two Juno values are
   equal. 


IMPORT Wr, Word, Formatter, Real AS R;

TYPE
  T = REFANY;
  (* Null | TEXT | REF Real | REF Pair *)

  Null <: T;
  Pair = RECORD car, cdr: T END;

 The following three declarations control the precision of Juno-2's
   calculations. Currently they are set to use single precision. 


TYPE
  Real = REAL;

CONST Zero = 0.0;

VAR HalfEps: Real;

 Zero and HalfEps are the zero and the relative error for type
   Real. That is, the difference between a real number x and
   the result of rounding it to a Real is at most HalfEps*x.
   HalfEps is initialized in the body of the JunoValue module. 


VAR (*CONST*)
  Nil: Null;

 The Juno value NIL is stored uniquely in the global variable Nil. 


CONST Prec: CARDINAL = R.MaxSignifDigits - 1;

PROCEDURE Unparse(wr: Wr.T; x: T; width: CARDINAL := 75; prec := Prec)
  RAISES {Wr.Failure};

 Pretty-print the value x to wr to a line width of width. Real numbers
   are unparsed to prec digits of precision. 

PROCEDURE UnparseToFmt(f: Formatter.T; x: T; prec := Prec) RAISES {Wr.Failure};

 Pretty-print the value x to the formatter f. The formatter is neither
   flushed nor closed by this procedure. Real numbers are unparsed to prec
   digits of precision. 

PROCEDURE Equal(READONLY x, y: T): BOOLEAN;
PROCEDURE Hash(READONLY k: T): Word.T;

 Equality and hash procedures on Juno values. 
 The following procedures return the sine, cosine, tangent, arc-sine,
   arc-cosine, arc-tangent, exponential, natural logarithm, and square root of
   the JunoValue.Real x. Ln returns NaN if x <= 0.0, and Sqrt returns
   NAN if x < 0.0. 


PROCEDURE Sin(x: Real): Real;
PROCEDURE Cos(x: Real): Real;
PROCEDURE Tan(x: Real): Real;
PROCEDURE Asin(x: Real): Real;
PROCEDURE Acos(x: Real): Real;
PROCEDURE Atan(y, x: Real): Real; (* arc-tangent of "y/x" *)
PROCEDURE Exp(x: Real): Real;
PROCEDURE Ln(x: Real): Real;
PROCEDURE Sqrt(x: Real): Real;

PROCEDURE RefReal(x: Real): REF Real;

 Return a REF Real with value x. 

PROCEDURE NewPoint(x, y: Real): REF Pair;

 Return a pair of the numeric values x and y. 

PROCEDURE ListFromVals(READONLY v: ARRAY OF T): T;

 Return the list containing the values of v. 

PROCEDURE IsList(v: T): BOOLEAN;

 RETURN TRUE iff v is a (non-empty) list. 

END JunoValue.