Wren Pt1, Closures, Vars, and Classes, the Language of EOS

Sources

My first Wren Article got me excited enough to try Wren out. If you like this, please do not forget to like the motivating article. It is also where I first saw the phrase Language of EOS.

Wren.io was a big help, as it has the
(in)complete documentation for the language.

The single best source for information about Wren, as a language, has been its tests. They are sparse, but do a better job explaining constructors, closures, etc etc than the documentation.

WARNING

I invest in EOS, I have bias motivations :)

Coming From a C-Family Language

Unless you have been programming Fortran 67 or Whitespace, this language should feel pretty familiar. Its documentation claims similarities to Ruby, of which I have never programmed, but I have heard it is like a majestic, ruby encrusted sword...

So You Want to Close Over?

Whenever I have heard someone attempt to explain closures they tend to contain the following phase.

"...the variables you want to close over..."

It would be good to review the available closure tests before proceeding. Wren’s Closure Tests.

If you are unfamiliar with closures you can have a basic review here

Quick Breakdown

	Functions	Class instance methods	Class static methods
1. vars declared in outer scope	✓ (exception: look at point 1)	✘	✘
2. import statements	✓	✓	✓
3. other classes (order of execution does not matter)	✓	✓	✓

1. Variables Declared in Outer Scope

Wren supports this feature with two exceptions.

1. A function cannot reference itself unless the Fn.new {...} and var x = statements exist on different lines.

The following simple function is an example where the wren file cannot compile due to the factorial reference within the factorial closure.

System.print(“Test”)
var factorial = Fn.new {|n|
    if (n == 1) {
        return 1
    }
    return n * factorial.call(n - 1)
}
System.print(factorial.call(5))

Upon execution you will get the following error.

[main line 5] Error at 'factorial': Undefined variable.

Notice there is no output of Test from the System.print line.

As mentioned above, to fix this move the var declaration to its own line.

System.print(“Test”)
var factorial = null
factorial = Fn.new {|n|
    if (n == 1) {
        return 1
    }
    return n * factorial.call(n - 1)
}
System.print(factorial.call(5))

The output this time is

Test
120

Great Success!

1. Class methods cannot reference outer scope vars.

The following code shows that referencing outside variables will fail whether in static or instance method.

var testing = 5
class Test {
    construct new() {}
    echo() {
        System.print(testing)
    }
    static echo() {
        System.print(testing)
    }
}

Test.echo();
Test.new().echo();

2. Import statements

They can be referenced from method or closure

3. Other classes

Classes and functions can reference other classes regardless of declaration order.

Here is a small script outlining the different, out-of-order references to classes that seem to work. As a side note, the output of Random surprised me, so I thought I would keep it in there. A little exercise for the reader.

import "random" for Random

var fn = Fn.new {
    System.print("From fn")
    OtherClass.echo()
}

class OtherClass {
    static echo() {
        System.print("From OtherClass")
        EchoClosureValues.new().echo()
    }
}

class EchoClosureValues {
    construct new() {}

    workingEcho() {
        System.print("Working Echo")
    }

    echo() {
        System.print("instance echo")
        System.print(Random.new().int(10))
    }
    static echo() {
        System.print("static echo")
        OtherClass.echo()
    }
}

// Toggle with comments
fn.call()
EchoClosureValues.echo()
EchoClosureValues.new().echo()

The output is

From fn
From OtherClass
instance echo
6
static echo
From OtherClass
instance echo
6
instance echo
6

In The End

Wren is a neet little language with few features. Unfortunately this does worry me for writing enterprise level software. As of the time of writing this article, I cannot find a Math class. To do a binary search, my floor operation looked like ~~. If you are confused by that or do not know the potential pitfalls of such an integer bitwise operation, then go forth and read! I hope EOS is not stunted by the language of choice.