The script does not always return "last"

[radpopl]

Shouldn't "last" be returned by default by the script?
If I swap the lines, the script works fine.

[this-username-is-already-taken]

It's always worked that way. For example, the full syntax for the following:

ColorBars()
GS = GreyScale()

would be

last = ColorBars()
GS = GreyScale(last)

So last itself isn't automatically returned, but it is automatically updated by Avisynth and used as the first argument for a function that expects it to be a clip (if you don't specify one yourself).

Similar to your example, the following output would be a video (ColorBars) if you manually added 'last' or 'return last' to line 3 of your script.

ColorBars()
GS = GreyScale()
last # or return last

The result would be the same as:

CB = ColorBars()
GS = GreyScale(CB)
CB # or return CB etc.