using diff() in a program

[DrD]

Code:


EXPORT ABCD()
BEGIN
  LOCAL a;
  INPUT({{a,[2]}}); //  You don't need to quote your input, since type [2] is a string var
  //F9:="3*X+1";
  RETURN diff(EVAL(a),X);  //  You need to EVAL(a).
END;

Use: 3*X+1 as input to a ==> returns 3