(* I have to write the formula twice.
A constraint system would avoid this,
at the cost of a lot of complexity elsewhere. *)
MODULE TempConv;
  IMPORT Texts, Oberon;

  VAR W: Texts.Writer;

  (* Scan both INTEGER and REAL numbers *)
  PROCEDURE ScanNum(): REAL;
    VAR result: REAL;
      S: Texts.Scanner;
  BEGIN Texts.OpenScanner(S, Oberon.Par.text, Oberon.Par.pos); Texts.Scan(S);
    IF S.class = Texts.Int THEN
      result := FLT(S.i)
    ELSIF S.class = Texts.Real THEN
      result := S.x
    ELSE
      result := 0.0
    END; RETURN result
  END ScanNum;

  PROCEDURE CToF*;
    VAR f: REAL;
  BEGIN f := ScanNum() * 9.0 / 5.0 + 32.0;
    Texts.WriteRealFix(W, f, 1, 1); Texts.WriteLn(W);
    Texts.Append(Oberon.Log, W.buf)
  END CToF;

  PROCEDURE FToC*;
    VAR c: REAL;
  BEGIN c := (ScanNum() - 32.0) * 5.0 / 9.0;
    Texts.WriteRealFix(W, c, 1, 1); Texts.WriteLn(W);
    Texts.Append(Oberon.Log, W.buf)
  END FToC;

BEGIN Texts.OpenWriter(W)
END TempConv.