From 618c9599563fd76d1ddeae32a1c0870764fc036e Mon Sep 17 00:00:00 2001
From: Manos Koukoutos <emmanouil.koukoutos@epfl.ch>
Date: Mon, 20 Jul 2015 01:47:04 +0200
Subject: [PATCH] Unapply in docs, List. List.headOption
---
doc/purescala.rst | 36 ++++++++++++++++++++++---------
library/collection/List.scala | 14 ++++++++++++
library/lang/string/package.scala | 2 +-
3 files changed, 41 insertions(+), 11 deletions(-)
diff --git a/doc/purescala.rst b/doc/purescala.rst
index bde72673c..f26a5e228 100644
--- a/doc/purescala.rst
+++ b/doc/purescala.rst
@@ -182,16 +182,32 @@ Pattern matching
.. code-block:: scala
expr match {
- // Simple (nested) patterns:
- case CaseClass( .. , .. , ..) => ...
- case v @ CaseClass( .. , .. , ..) => ...
- case v : CaseClass => ...
- case (t1, t2) => ...
- case 42 => ...
- case _ => ...
-
- // can also be guarded, e.g.
- case CaseClass(a, b, c) if a > b => ...
+ // Simple (nested) patterns:
+ case CaseClass( .. , .. , ..) => ...
+ case v @ CaseClass( .. , .. , ..) => ...
+ case v : CaseClass => ...
+ case (t1, t2) => ...
+ case 42 => ...
+ case _ => ...
+
+ // can also be guarded, e.g.
+ case CaseClass(a, b, c) if a > b => ...
+ }
+
+Custom pattern matching with ``unapply`` methods are also supported:
+
+.. code-block:: scala
+
+ object :: {
+ def unapply[A](l: List[A]): Option[(A, List[A])] = l match {
+ case Nil() => None()
+ case Cons(x, xs) => Some((x, xs))
+ }
+ }
+
+ def empty[A](l: List[A]) = l match {
+ case x :: xs => false
+ case Nil() => true
}
Values
diff --git a/library/collection/List.scala b/library/collection/List.scala
index c7a38dc63..b3078c600 100644
--- a/library/collection/List.scala
+++ b/library/collection/List.scala
@@ -35,6 +35,11 @@ sealed abstract class List[T] {
(that != Nil[T]() || res == this)
}
+ def headOption: Option[T] = this match {
+ case Nil() => None[T]()
+ case Cons(h, _) => Some(h)
+ }
+
def head: T = {
require(this != Nil[T]())
val Cons(h, _) = this
@@ -537,6 +542,15 @@ object ListOps {
case class Cons[T](h: T, t: List[T]) extends List[T]
case class Nil[T]() extends List[T]
+// 'Cons' Extractor
+object :: {
+ def unapply[A](l: List[A]): Option[(A, List[A])] = l match {
+ case Nil() => None()
+ case Cons(x, xs) => Some((x, xs))
+ }
+}
+
+
@library
object ListSpecs {
def snocIndex[T](l : List[T], t : T, i : BigInt) : Boolean = {
diff --git a/library/lang/string/package.scala b/library/lang/string/package.scala
index f09af7c6e..e3cd3d7ae 100644
--- a/library/lang/string/package.scala
+++ b/library/lang/string/package.scala
@@ -16,7 +16,7 @@ package object string {
@ignore
def listToList[A](s: ScalaList[A]): List[A] = s match {
- case h :: t =>
+ case scala.::(h, t) =>
Cons(h, listToList(t))
case _ =>
Nil[A]()
--
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