Positive: There is an Oz tutorial started at eclectic
Warning: since Unicode there is no longer a single quote and a dbl-quote character: just as the left-Alt key was never the same scan code as the right-Alt key. In all that follows, copy the code into a reliable ANSI code editor and flip all ’single’ quotes to an ANSI apostrophe as on an American ASCII QWERTY keyboard and all dbl quotes to a SHIFT-apostrophe. Otherwise you are left with left single quotes, right-single quotes, left-dbl-quotes and right-dbl-quotes which will cause errors in Mozart. Do not use ‘back-tick’ (unshifted-~) as your apostrophe character.
You should not have to be a Prolog programmer to learn Oz, but short of being one already, what sense could you make of the errors you will encounter trying to follow the introduction to compiling an Oz application? The ‘Aufhebung’ issue again. Or you must almost know it just to learn it.
Here goes.
In Rebol you would just script it so:
write %dump.txt read http://localhost:8080/perl/get_env.prl
But in Oz you will need to compile to a functor, so let’s get started on the tutorial’s Webget.oz
You will need to wrap the file as a functor, so we start with
functor
end
We will open STDIN and STDOUT so we need Open and this will be an Application so we will import both:
functor
import
Application
Open
end
What follows is the code from the tutorial which will not compile (not in OPI, not on a cmd line):
functor
import
Application
Open
define
Args = {Application.getArgs record('in'(single type:string)
'out'(single type:string))}
Status = try
I={New Open.file init(url: Args.'in')}
O={New Open.file init(name: Args.'out'
flags:[write create truncate])}
in
local
proc { Copy}
S={I read(list:$)}
in
if S=="" then
{O write(vs:S)} { Copy}
end
end
in
{ Copy}
end
catch _ then 1
end
{Application.exit Status}
end
The warning we will receive will be an arity mismatch for Copy.
I experimented with {CopyWWW _} and with {CopyWWW X} in place of {Copy}
Running ozc -c in TextPad compiles succesfully by using {Copy _} in the first 2 occurences of {Copy}. Ditto for selecting ‘Compile File’ on the emacs oz menu.
Now on to compiling that oza file.
To get the oza file I had to use a cmd session:
ozc -c Webget.oz -o Webget.oza
Otherwise compiling (in TextPad or emacs) gave me just Webget.ozf
Now I could run the ozengine against a web page:
ozengine Webget.oza --in http://localhost:8080/perl/get_env.prl --out dump.txt
The program will only exit with CTRL-C CTRL-C and leaves file handles open but if you are content to run it just once
type dump.txt
Oops… no file?
We back track by revisiting the code.
functor
import
Application
Open
Show ; we will try to Show Status
define
Args = {Application.getArgs record(
'in'(single type:string)
'out'(single type:string))} ;; variable names are words
Status = try
In={New Open.file init(url: Args.'in')}
Out={New Open.file init(name: Args.'out'
flags:[write create truncate])}
in
local
proc { Copy}
Str={In read(list:$)} ;; lhs var name is now a word
in
if Str=="" then
{Out write(vs:Str)} { Copy}
end
{In close}
{Out close}
end
in
{ Copy}
end
0 ;; this was a missing ZERO as in 'success' ?
;; (given that a ONE follows next on error)
catch _ then
{Show Status}
1 ;; any exception is failure -
;; was the file readonly?
end
{Application.exit Status} ;; Status remains unknown
end
Now we compile without ARITY issues … but still fail to write a file …
So now to look at file IO.
Hmm. The file io.oz offered for our edification has no error handling.
We try Webget2.oz for local disk files as follows:
functor
import
Application Open
define
Args = {Application.getArgs record('in' (single type:string)
'out' (single type:string))}
Status = try
In={New Open.file init(name: Args.'in')}
Out={New Open.file init(name: Args.'out'
flags:[write create truncate])}
in
local
proc { Copy }
Str={In read(list:$)}
in
if Str=="" then
{Out write(vs:Str)}
{ Copy }
end
{In close}
{Out close}
end
in
{ Copy }
end
0
catch _ then
1
end
{Application.exit Status}
end
Which works great so the issue is reading the URL … It comes up in the browser and Rebol reads it fine as follows:
write %dump.txt “” ; we nix that file
write %dump.txt read http://localhost:8080/perl/get_env.prl
in a Rebol shell. So
if Str\=”" then
must be non-terminating for some URL’s on Win32. So we will read the whole URL first.
Now, how to iterate over a list … and then we start back at Lists and progress to the list module
