The Pizza Compiler

The Pizza language is an extension to Java with three new features:
- Generics (aka Parametric polymorphism)
- Function pointers (aka First-class functions)
- Class cases and pattern matching (aka Algebraic types)

 Pizza Example: Enumeration

 

 

 

package net.sf.pizzacompiler.util; /** an abstract class for implementations of the Enumeration interface */ public abstract class Enumerator<A> implements Enumeration<A> { /** the Enumeration methods */ public abstract boolean hasMoreElements(); public abstract A nextElement(); /** concat another enumerator, to be called when this one is done */ public Enumerator<A> concat(Enumerator<A> rest) { return new CompositeEnumerator(this, rest); } /** return enumerator that yields `f' applied to each element * of this enumerator */ public <B> Enumerator<B> map((A)->B f) { return new MapEnumerator(f, this); } /** return elements of this enumerator as long as predicate `p' is true */ public Enumerator<A> takeWhile((A)->boolean p) { return new TakeWhileEnumerator(p, this); } /** return enumerator that starts with the first element of this * enumerator for which `p' holds, and then continues with all * subsequent elements of this enumerator */ public Enumerator<A> dropWhile((A)->boolean p) { return new DropWhileEnumerator(p, this); } /** return enumerator that yields all element of this enumerator that * satisfy predicate `p'. */ public Enumerator<A> filter((A)->boolean p) { return new FilterEnumerator(p, this); } /** apply function `f' to all elements of this enumerator */ public <B> void forall((A)->B f) { while (hasMoreElements()) f(nextElement()); } /** reduce all elements of this enumerator with binary operation `f', * starting with `z'. Operations are grouped to the left. */ public <B> B reduceLeft(B z, (B,A)->B f) { while (hasMoreElements()) z = f(z, nextElement()); return z; } /** reduce all elements of this enumerator with binary operation `f', * starting with `z'. Operations are grouped to the right. */ public <B> B reduceRight((A,B)->B f, B z) { if (hasMoreElements()) return f(nextElement(), reduceRight(f, z)); else return z; } } /** an enumerator implementing `map' */ class MapEnumerator<B,A> extends Enumerator<A> { private (B)->A f; private Enumerator<B> dom; MapEnumerator((B)->A f, Enumerator<B> dom) { this.f = f; this.dom = dom; } public boolean hasMoreElements() { return dom.hasMoreElements(); } public A nextElement() { return f(dom.nextElement()); } } /** an enumerator implementing `filter' */ class FilterEnumerator<A> extends Enumerator<A> { private (A)->boolean p; private Enumerator<A> dom; private A next; private boolean lookahead; FilterEnumerator((A)->boolean p, Enumerator<A> dom) { this.p = p; this.dom = dom; lookahead = false; } public boolean hasMoreElements() { while (!lookahead && dom.hasMoreElements()) { next = dom.nextElement(); lookahead = p(next); } return lookahead; } public A nextElement() { if (lookahead || hasMoreElements()) { lookahead = false; return next; } throw new NoSuchElementException(); } } /** an enumerator implementing `takewhile' */ class TakeWhileEnumerator<A> extends Enumerator<A> { private (A)->boolean p; private Enumerator<A> dom; private A next; private boolean lookahead; TakeWhileEnumerator((A)->boolean p, Enumerator<A> dom) { this.p = p; this.dom = dom; lookahead = false; } public boolean hasMoreElements() { if (!lookahead && dom.hasMoreElements()) { next = dom.nextElement(); if (p(next)) lookahead = true; else dom = EmptyEnumerator.empty; } return lookahead; } public A nextElement() { if (lookahead || hasMoreElements()) { lookahead = false; return next; } throw new NoSuchElementException(); } } /** an enumerator implementing `dropwhile' */ class DropWhileEnumerator<A> extends Enumerator<A> { private (A)->boolean p; private Enumerator<A> dom; private A next; private boolean lookahead; DropWhileEnumerator((A)->boolean p, Enumerator<A> dom) { this.p = p; this.dom = dom; lookahead = false; } public boolean hasMoreElements() { while (p != null && dom.hasMoreElements()) { next = dom.nextElement(); if (!p(next)) { lookahead = true; p = null; } } return lookahead || dom.hasMoreElements(); } public A nextElement() { if (lookahead || p != null && hasMoreElements()) { lookahead = false; return next; } else { return dom.nextElement(); } } }