Re: Strange Bug with numeric double constants

[thompson(at)orpheus.nascom.nasa.gov (William Thompson)]

Alex Schuster <alex@rosa.mpin-koeln.mpg.de> writes:

>Hi!

>I just experienced some weird IDL behaviour:

>IDL> help, 1.0d+2.0d

>help, 1.0d+2.0d
>             ^
>% Syntax error.

>IDL> help, 1d+2d

>help, 1d+2d
>           ^
>% Syntax error.

>Strange, isn't it? There's no problem with byte constants: 

>IDL> help, 1b+2b
><Expression>    BYTE      =    3

>An additional blank helps:

>IDL> help, 1d +2d
><Expression>    DOUBLE    =        3.0000000

>I didn't try IDL 5.2, but it happened with 4.0 and 5.1 on Unix and
>Windows. I guess IDL expects an exponential notation like 1d0, and is
>confused by the nonnumeric plus character.



Wouldn't it be more proper to write these numbers as

	IDL> help, 1.0d0+2.0d0

As others have pointed out, IDL is getting confused by putting the +2
immediately after the "d"--it thinks it's part of the exponent.  I guess that
IDL usually knows what you meant if you leave the exponent off, but not always
as you found out.

Cheers,

William Thompson