Undoc'd Feature?

[toml_12953]

(07-03-2022 09:14 AM)Wes Loewer Wrote:  It's hard to trace exactly what is happening in the code without knowing the values in list A, but are you sure that it's actually decrementing?

When I use --X in an HPPL program, or on the Home screen, it is interpreted as -(-X), the negative of the negative of X. Likewise, ---X is -(-(-X)).

In CAS programs (with #cas ... #end), or on the CAS screen, it does allow a++ and a-- but not ++a or --a.

I don't know if this is considered a bug, but in CAS a++ is really doing ++a, incrementing BEFORE evaluating the expression. Likewise for a--. Same behavior in xcas. Maybe it's documented somewhere, but I couldn't find it.

When I substitute the -- notation for the original code, the program gives the same answer! If it's not actually doing a decrement, it's an awfully big coincidence that it should still work the same, no?

Original code:

Code:

 
Y:=Y-1;
T:=A(X)-A(Y);
IF T==0 OR X-Y==ABS(T) THEN
  Y:=0;
  A(X):=A(X)-1;
  WHILE A(X)==0 DO
    X:=X-1;
    A(X):=A(X)-1;
  END;
END;