Recursion and Pattern Matching

[Omer Eltoum]

Hi.

I have the following code:

module main

require `java.net.Socket`
require `java.io.BufferedReader`
require `java.io.InputStreamReader`

connect ->
    print(read(reader))
    where
        socket: new Socket('irc.qt.io', 6667)
        reader: new BufferedReader(new InputStreamReader(socket.getInputStream()))

read(reader) ->
    parse(reader.readLine()),
    read(reader)
    where
        parse(line) =>
            Nothing : ''
            * : line

main ->
    connect()

What I'm trying to do is in read(reader), read a line from the BufferedReader and, if it is Nothing, return '' and return the line otherwise.
I'm getting 2 errors here:

Firstly, the error I get when trying to recur (parse(reader.readLine()), read(reader)) is:

Exception in thread "main" java.lang.VerifyError: (class: main, method: read signature: (Ljava/lang/Object;)Ljava/lang/Object;) Inconsistent stack height 1 != 0
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2442)
    at java.lang.Class.getDeclaredMethod(Class.java:1952)
    at loop.Executable.main(Executable.java:232)
    at loop.Loop.safeEval(Loop.java:71)
    at loop.Loop.run(Loop.java:41)
    at loop.Loop.main(Loop.java:26)

The error I get with the pattern matching is:

Exception in thread "main" java.lang.NullPointerException
    at loop.AsmCodeEmitter.emitTypePatternRule(AsmCodeEmitter.java:1544)
    at loop.AsmCodeEmitter.access$1300(AsmCodeEmitter.java:68)
    at loop.AsmCodeEmitter$27.emitCode(AsmCodeEmitter.java:1474)
    at loop.AsmCodeEmitter.emit(AsmCodeEmitter.java:235)
    at loop.AsmCodeEmitter.emitChildren(AsmCodeEmitter.java:224)
    at loop.AsmCodeEmitter.access$200(AsmCodeEmitter.java:68)
    at loop.AsmCodeEmitter$18.emitCode(AsmCodeEmitter.java:1121)
    at loop.AsmCodeEmitter.emit(AsmCodeEmitter.java:235)
    at loop.AsmCodeEmitter$18.emitCode(AsmCodeEmitter.java:1010)
    at loop.AsmCodeEmitter.emit(AsmCodeEmitter.java:235)
    at loop.AsmCodeEmitter.write(AsmCodeEmitter.java:166)
    at loop.Executable.compile(Executable.java:279)
    at loop.Loop.loopCompile(Loop.java:98)
    at loop.Loop.run(Loop.java:38)
    at loop.Loop.main(Loop.java:26)

This is all done through a file. Since there's no IDE plugin as of yet, I use this little script:

public class Run {
    public static void main(String[] args) throws Exception {
        Process process = Runtime.getRuntime().exec("java -jar lib/loop.jar src/Main.loop");
        BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
        BufferedReader error = new BufferedReader(new InputStreamReader(process.getErrorStream()));

        String line;
        while ((line = input.readLine()) != null)
            System.out.println(line);
        line = "";
        while ((line = error.readLine()) != null)
            System.out.println(line);
    }
}

I have no idea what I'm doing wrong. Do you guys understand?
The equivalent Java code would probably be:

public String read(BufferedReader reader) {

String line = reader.readLine();
if (line == null)

return "";

else

return line;

}

But how would I recur, since there are no loops?

Thanks,
Omer

[Dhanji R. Prasanna]

Hmm, that's not good. Let me take a closer look. Our latest version has changed the syntax for imports and local variable assignments (allows you to write them in a sequence). So this will look slightly different.

Will get back to you soon.