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:

void main(Array<String> args) {
  println("Hello world!");
}

You can now generate Java code from this program using:

pilc -i hello.pil --java

or Python code:

pilc -i hello.pil --python

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):

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

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:

$ 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!

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):

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));
}

And running it:

$ 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}

-- ZefHemel - 02 Oct 2009