shebang_mod - a modification to AviSynth to implement script pre-processing

[wonkey_monkey]

Download: shebang_mod.zip

• Now based on Avisynth+ 3.7.2

As mentioned here, I had an idea to add a script pre-processor to AviSynth to allow for plugins that could free up the grammar a bit, or perform other tricks, while maximising backwards compatability and not putting any new restrictions on script writers or AviSynth itself.

I've managed to make it work with a short modification to scriptparser.cpp. Compiled AviSynth DLLs (based on 3.7.2 from https://github.com/AviSynth/AviSynthPlus) are in the zip file above along with an example preprocessing plugin (ScriptMonkey.dll) and a couple of example scripts, as well as the modified scriptparser.cpp and a diff file.

Preprocessing is triggered by a shebang ("#!") as the first characters of the first (and any immediately following) lines of the script, followed by the name of any function which takes a string as input and returns a string (the function name can be optionally followed by comments, as below):

#!revstr <- this internal AviSynth function reverses the characters of the script (including the order of lines)

21VYoTtrevnoC
srabroloC

As a more useful example, the included ScriptMonkey plugin reformats scripts so you no longer need to use backslashes to continue lines (within function parameter lists only), and allows inter-parameter # comments and trailing commas, so function parameters can be quickly and easily commented out:

#!ScriptMonkey <- this line enables the script

# The ScriptMonkey plugin function allows multi-line parameters without
# requiring backslashes (\) for line continuation, # comments in the middle of
# multi-line parameters, and trailing commas in parameter lists.

ColorBarsHD

ConvertToYV12(
	interlaced = true,
	matrix = "rec709", # this trailing comma is now allowed
#	chromaresample = "point" # this parameter is commented out
)

I put it together pretty quickly so if anyone wants to look at the source code and see if I've made any mistakes I'd appreciate it.

[Ceppo]

I kinda like the idea. Thanks a lot. I will make some tests when I'm free.

[wonkey_monkey]

Updated from Avisynth+ 3.7.2.

[pinterf]

Can you remember what is the reason for requiring backslash for line continuation? I know - compatibility and probably handling some special function calling case. Surely there were discussions about it, Avisynth is mature enough.

[wonkey_monkey]

Nope, no idea. I did some Googling a few weeks back while I was working on this, and all I could find was an obscure case, that Gavino came up with I think, where getting rid of the backslash requirement could cause a change to the result of a script. It was something like

some_var = -5
+ 5 ? clip1 : clip2

Currently, some_var would equal 5 and clip1 would become implicit last. If lines auto-continued, some_var would be equal to clip2.

However, just to be on the safe side, my mod and filter only removes newlines while inside function parameter lists.

[StainlessS]

Originally Posted by pinterf

Can you remember what is the reason for requiring backslash for line continuation?

Originally Posted by wonkey_monkey

all I could find was an obscure case, that Gavino came up with

Not sure if this is same pre recent Avs+,

# OK

Function Fn() { return true }

x=Round(123.456)
(TRUE) ? Fn() : NOP     # On separate line OK

return MessageClip("DONE")

Not OK

Function Fn() { return true }

x=Round(123.456)         (TRUE) ? Fn() : NOP   # "Script Error. 'Int' cannot be called. Give me A function!"

return MessageClip("DONE")

I sometimes like to pack a few things on a single line, so as to be easy to comment/uncomment the lot, during debug.

EDIT: Shifting NOP out of it, same.

Function Fn() { return true }

x=Round(123.456)         (TRUE) ? Fn() : Fn()   # "Script Error. 'Int' cannot be called. Give me A function!"

return MessageClip("DONE")

EDIT: Maybe I'm doin' something silly, its 05:45 and I aint been to bed yet. [maybe to do with the new function objects or whatever they are ???]

EDIT: Bit more of a clue,

Function Fn() { return true }

x=Float(123)         (TRUE) ? Fn() : Fn()    # "Script Error. 'float' cannot be called. Give me A function!"

return MessageClip("DONE")

Looks maybe something like "123.0(TRUE)" , some kind of Parser bug.

[StainlessS]

Further to above, no error,[removed () from around (TRUE) ]

Function Fn() { return true }

x=Float(123)         TRUE ? Fn() : Fn()    # NO ERROR

return MessageClip("DONE")