First off thank you for your help. When I tried to run that
interactive.ijsscript it wouldn't work. It said:
cd x:\path\to\j\root\
jconsole ~temp\interactive.ijs
|spelling error
| jconsole ~temp\interactive.ijs
| ^
i checked the spelling with the name I saved it as and they were the same.
On 4/12/07, Dan Bron <[EMAIL PROTECTED]> wrote:
> I am new to J programming, and I don't quite understand script files.
Script files are just your source code. J scripts (*.ijs) are analogous
to C programs (*.c). However, whereas C is compiled, J is interpreted, so
there's no need for a separate compilation step (or linking, or header
files, or memory allocation....).
> How do you write the equivalent of a main function from C programming?
J programs don't have a standard entry point. They have no equivalent to
a "main function". When you feed a script to J, it executes it line by
line, so the first instruction you give it will the first instruction it
executes.
To run a J program from the command line, you simply type
jconsole my_program.ijs
what happens after that depends on the instructions in the script.
> I don't want to define a verb. I simply want to create a main program
Programs consist of functions, and all functions in J are verbs. You
cannot write a (useful) program without defining a verb.
> where I can query the user and except user input.
The instructions to query the user and printing a response will be a
verb. All functions in J are verbs.
Having said that: be aware that J is block, not stream oriented.
That is, J's strength lies in processing all the data at once. That
implies that it must have all the data in advance and consequently that it
is poorly suited for interactive tasks.
Since you're new to J, if I were you, I would choose a programming problem
that would play to J's strengths, to acquire a flavor of the language (and
reasons why someone would choose it over others).
And, since familiar with C, I'd recommend that you read through Henry
Rich's excellent "J for C programmers" at
http://www.jsoftware.com/help/jforc/contents.htm .
All the preceding isn't to say that interactive programs in J are not
possible. They are. In fact, they come in two flavors: command line and
GUI. GUI solutions are by far the easiest and most prevalent method for
user interaction in J, and that's the road I would recommend for you. Take
a look at the menu item Edit>Form Editor .
Command line solutions, while less common, are still possible (but are
somewhat involved). To get started, download this script:
http://www.jsoftware.com/svn/DanBron/trunk/general/r_pl.ijs
and save it in the "temp" directory under your J installation. Then,
create a new script in that same directory, and name it "interactive.ijs". This
should be the contents of interactive.ijs :
require '~temp\r_pl.ijs strings'
query =: verb define
y =. deb tolower y
if. 'quit' -: deb tolower y do.
0 ; 'bye!'
else.
_ ; 'Why do you say "', y , '"?'
end.
)
echo 'Welcome to psychotherapy!'
query r_plx ''
Now, open a command prompt:
> cd x:\path\to\j\root\
> jconsole ~temp\interactive.ijs
Welcome to psychotherapy!
Hi.
Why do you say "Hi."?
To greet you.
Why do you say "To greet you."?
Because you asked me why I said `Hi'.
Why do you say "Because you asked me why I said `Hi'."?
You're a jerk.
Why do you say "You're a jerk."?
quit
bye!
-Dan
PS: Another reason that interactive programs aren't the norm in J is
because J subscribes to the philosophy of functional
programming. Functional programs disdain side effects, which is exactly
what asynchronous events like user interaction are.
Which doesn't mean you can't write an asynchronous program in J; to the
contrary, I earned my living for 3 years with such a system (though the
events came over sockets, not from user input).
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