---++ A simple PIL tutorial

PIL is a language based on a small subset of Java, but simpler and with a few subtle differences and convenient additions. Let's start with the famous "Hello world!" example. Create a new file _hello.pil_:
<verbatim>
void main(Array<String> args) {
  println("Hello world!");
}
</verbatim>

You can now generate Java code from this program using:
<verbatim>
pilc -i hello.pil --java
</verbatim>
or Python code:
<verbatim>
pilc -i hello.pil --python
</verbatim>
Code is generated in the _out/_ directory, optionally this destination directory can be set with the -d switch.

Both the Python and Java back-ends need a small run-time library to run the software. In the case of Java you can compile and run the generated code using (assuming you installed it with Nix, otherwise, replace the path):
<verbatim>
javac -cp out:/nix/store/*-pil-*/share/pil/pil.jar application/Main.java
java -cp out:/nix/store/*-pil-*/share/pil/pil.jar application.Main
</verbatim>
But, because this is kind of annoying for simply testing, the PIL distribution comes with convenient _pil-java_ and _pil-python_ wrapper scripts that compile and run the program for you:
<verbatim>
$ pil-java hello.pil
[ pilc | info ] Now compiling: hello.pil
[ pilc | info ] Done with hello.pil
Hello world!
$ pil-python hello.pil
[ pilc | info ] Now compiling: hello.pil
[ pilc | info ] Done with hello.pil
Hello world!
</verbatim>

---++ Word frequency
You will have noticed that unlike Java, PIL also support global function, i.e. methods that are not part of a class. Here is a slightly more complicate example that also uses the simple type inferencing features of PIL (the _var_ keyword):
<verbatim>
List<String> cutIntoWords(String text) {
  var i = 0;
  var words = new List<String>();
  var word = new MutableString();
  while(i < text.length) {
	 if(text[i] == ' ') {
		words.add(word.as<String>);
		word = new MutableString();
		while(text[i] == ' ') {
		  i = i + 1;
		}
	 } else {
		word.append(text[i]);
		i = i + 1;
	 }
  }
  words.add(word.as<String>);
  return words;
}

Map<String, Int> wordFrequency(String text) {
  var words = cutIntoWords(text);
  var freq = new Map<String, Int>();
  for(String word : words) {
	 if(freq.contains(word)) {
		freq[word] = freq[word] + 1;
	 } else {
		freq[word] = 1;
	 }
  }
  return freq;
}

void main(Array<String> args) {
  var sentence = "This a sentence and I wonder if it can calculate the word frequency of each of these words and if it works";
  println(sentence);
  println(wordFrequency(sentence));
}
</verbatim>
And running it:
<verbatim>
$ pil-java parseSentence.pil
[ pilc | info ] Now compiling: parseSentence.pil
[ pilc | info ] Done with parseSentence.pil
This a sentence and I wonder if it can calculate the word frequency of each of these words and if it works
{it=2, can=1, calculate=1, a=1, sentence=1, the=1, frequency=1, This=1, I=1, works=1, and=2, of=2, words=1, if=2, wonder=1, word=1, each=1, these=1}
$ pil-python parseSentence.pil
[ pilc | info ] Now compiling: parseSentence.pil
[ pilc | info ] Done with parseSentence.pil
This a sentence and I wonder if it can calculate the word frequency of each of these words and if it works
{'a': 1, 'and': 2, 'works': 1, 'word': 1, 'calculate': 1, 'sentence': 1, 'This': 1, 'of': 2, 'it': 2, 'I': 1, 'frequency': 1, 'these': 1, 'can': 1, 'words': 1, 'each': 1, 'the': 1, 'if': 2, 'wonder': 1}
</verbatim>

-- Main.ZefHemel - 02 Oct 2009