Re: Re: Can anyone save my sanity -- help me to understand filtering?

[Graham Douglas]

Uwe, you're quite right, it was stupid of me not to

post an example and I apologise.

 

The basic functionality I want to achieve is the

ability to run an interpreted language called

Lua, with which I'd like to create PostScript graphics

-- EPS files. It is just an experiment but that's what

I'd like to do -- dynamic EPS generation.

 

OK, I think I may be getting somewhere... I compiled

Lout and found the line where system() is called. I

inserted a breakpoint and did a disk search for

a file called louti1, and found it. Examining the content

fixed part of the puzzle for me, I think, So here's my attempt

to explain what *I think* is happening. Please

tell me where I am wrong.

 

Suppose that I define something called @Lua:

 

def @Lua
right x
{
def @Filter {Lua @FilterIn > @FilterOut}
x
}

 

[[Aside: The command to run Lua is, not surprisingly,

"Lua". A command called "dofile(...)" makes Lua run

a file eg

 

dofile(foo.lua)

 

makes Lua run "foo.lua"]]

 

When I execute Lout with, say,

 

@Lua {
dofile("c:\\lua\\hello.lua")
}

 

then Lout creates a temporary file

(expands @FilterIn) called louti1

which then has the string

 

dofile("c:\\lua\\hello.lua")

 

written into it. Am I right so far?

 

Now, Lua is called with the CONTENTS of

this temporary file (louti1) as its argument so

Lua sees

 

Lua dofile("c:\\lua\\hello.lua")

 

and (with Lua) the output is written to stdout

by default which is then piped (correct term?)

to the second temporary file created from the

expansion of @FilterOut -- a temporary file

called lout1, or similar, is created for the purpose.

Lout then reads the content of lout1 and you're done?

 

Well, almost. The bit I still have to crack is how

to get Lout to do an @IncludeGraphic from

a situation where Lua outputs EPS code.

Working on that now but any pointers based

on the @Lua example about would be great.

 

Best wishes and thanks to all for

putting up with my troubles -- no pain, no gain I

guess (the gain had better be worth it ;-))

 

Thanks to all especially Uwe.

 

Graham