--- a/handouts/pep-ho.tex Fri Nov 10 09:00:46 2017 +0000
+++ b/handouts/pep-ho.tex Fri Nov 10 09:23:23 2017 +0000
@@ -588,182 +588,185 @@
like \code{print}.
-\subsection*{Cool Stuff}
+% \subsection*{Cool Stuff}
-The first wow-moment I had with Scala was when I came across
-the following code-snippet for reading a web-page.
+% The first wow-moment I had with Scala was when I came across
+% the following code-snippet for reading a web-page.
-\begin{lstlisting}[ numbers=none]
-import io.Source
-val url = """http://www.inf.kcl.ac.uk/staff/urbanc/"""
-Source.fromURL(url)("ISO-8859-1").take(10000).mkString
-\end{lstlisting}
+% \begin{lstlisting}[ numbers=none]
+% import io.Source
+% val url = """http://www.inf.kcl.ac.uk/staff/urbanc/"""
+% Source.fromURL(url)("ISO-8859-1").take(10000).mkString
+% \end{lstlisting}
-\noindent These three lines return a string containing the
-HTML-code of my webpage. It actually already does something
-more sophisticated, namely only returns the first 10000
-characters of a webpage in case it is too large. Why is that
-code-snippet of any interest? Well, try implementing
-reading-from-a-webpage in Java. I also like the possibility of
-triple-quoting strings, which I have only seen in Scala so
-far. The idea behind this is that in such a string all
-characters are interpreted literally---there are no escaped
-characters, like \verb|\n| for newlines.
+% \noindent These three lines return a string containing the
+% HTML-code of my webpage. It actually already does something
+% more sophisticated, namely only returns the first 10000
+% characters of a webpage in case it is too large. Why is that
+% code-snippet of any interest? Well, try implementing
+% reading-from-a-webpage in Java. I also like the possibility of
+% triple-quoting strings, which I have only seen in Scala so
+% far. The idea behind this is that in such a string all
+% characters are interpreted literally---there are no escaped
+% characters, like \verb|\n| for newlines.
-My second wow-moment I had with a feature of Scala that other
-functional programming languages do not have. This feature is
-about implicit type conversions. If you have regular
-expressions and want to use them for language processing you
-often want to recognise keywords in a language, for example
-\code{for},{} \code{if},{} \code{yield} and so on. But the
-basic regular expression \code{CHAR} can only recognise a
-single character. In order to recognise a whole string, like
-\code{for}, you have to put many of those together using
-\code{SEQ}:
+% My second wow-moment I had with a feature of Scala that other
+% functional programming languages do not have. This feature is
+% about implicit type conversions. If you have regular
+% expressions and want to use them for language processing you
+% often want to recognise keywords in a language, for example
+% \code{for},{} \code{if},{} \code{yield} and so on. But the
+% basic regular expression \code{CHAR} can only recognise a
+% single character. In order to recognise a whole string, like
+% \code{for}, you have to put many of those together using
+% \code{SEQ}:
-\begin{lstlisting}[numbers=none]
-SEQ(CHAR('f'), SEQ(CHAR('o'), CHAR('r')))
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% SEQ(CHAR('f'), SEQ(CHAR('o'), CHAR('r')))
+% \end{lstlisting}
-\noindent This gets quickly unreadable when the strings and
-regular expressions get more complicated. In other functional
-programming languages, you can explicitly write a conversion
-function that takes a string, say \dq{\pcode{for}}, and
-generates the regular expression above. But then your code is
-littered with such conversion functions.
+% \noindent This gets quickly unreadable when the strings and
+% regular expressions get more complicated. In other functional
+% programming languages, you can explicitly write a conversion
+% function that takes a string, say \dq{\pcode{for}}, and
+% generates the regular expression above. But then your code is
+% littered with such conversion functions.
-In Scala you can do better by ``hiding'' the conversion
-functions. The keyword for doing this is \code{implicit} and
-it needs a built-in library called
+% In Scala you can do better by ``hiding'' the conversion
+% functions. The keyword for doing this is \code{implicit} and
+% it needs a built-in library called
-\begin{lstlisting}[numbers=none]
-scala.language.implicitConversions
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% scala.language.implicitConversions
+% \end{lstlisting}
-\noindent
-Consider the code
+% \noindent
+% Consider the code
-\begin{lstlisting}[language=Scala]
-import scala.language.implicitConversions
+% \begin{lstlisting}[language=Scala]
+% import scala.language.implicitConversions
-def charlist2rexp(s: List[Char]) : Rexp = s match {
- case Nil => EMPTY
- case c::Nil => CHAR(c)
- case c::s => SEQ(CHAR(c), charlist2rexp(s))
-}
+% def charlist2rexp(s: List[Char]) : Rexp = s match {
+% case Nil => EMPTY
+% case c::Nil => CHAR(c)
+% case c::s => SEQ(CHAR(c), charlist2rexp(s))
+% }
-implicit def string2rexp(s: String) : Rexp =
- charlist2rexp(s.toList)
-\end{lstlisting}
+% implicit def string2rexp(s: String) : Rexp =
+% charlist2rexp(s.toList)
+% \end{lstlisting}
-\noindent where the first seven lines implement a function
-that given a list of characters generates the corresponding
-regular expression. In Lines 9 and 10, this function is used
-for transforming a string into a regular expression. Since the
-\code{string2rexp}-function is declared as \code{implicit},
-the effect will be that whenever Scala expects a regular
-expression, but I only give it a string, it will automatically
-insert a call to the \code{string2rexp}-function. I can now
-write for example
+% \noindent where the first seven lines implement a function
+% that given a list of characters generates the corresponding
+% regular expression. In Lines 9 and 10, this function is used
+% for transforming a string into a regular expression. Since the
+% \code{string2rexp}-function is declared as \code{implicit},
+% the effect will be that whenever Scala expects a regular
+% expression, but I only give it a string, it will automatically
+% insert a call to the \code{string2rexp}-function. I can now
+% write for example
-\begin{lstlisting}[numbers=none]
-scala> ALT("ab", "ac")
-res9 = ALT(SEQ(CHAR(a),CHAR(b)),SEQ(CHAR(a),CHAR(c)))
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% scala> ALT("ab", "ac")
+% res9 = ALT(SEQ(CHAR(a),CHAR(b)),SEQ(CHAR(a),CHAR(c)))
+% \end{lstlisting}
-\noindent Recall that \code{ALT} expects two regular
-expressions as arguments, but I only supply two strings. The
-implicit conversion function will transform the string into a
-regular expression.
+% \noindent Recall that \code{ALT} expects two regular
+% expressions as arguments, but I only supply two strings. The
+% implicit conversion function will transform the string into a
+% regular expression.
-Using implicit definitions, Scala allows me to introduce
-some further syntactic sugar for regular expressions:
+% Using implicit definitions, Scala allows me to introduce
+% some further syntactic sugar for regular expressions:
-\begin{lstlisting}[ numbers=none]
-implicit def RexpOps(r: Rexp) = new {
- def | (s: Rexp) = ALT(r, s)
- def ~ (s: Rexp) = SEQ(r, s)
- def % = STAR(r)
-}
+% \begin{lstlisting}[ numbers=none]
+% implicit def RexpOps(r: Rexp) = new {
+% def | (s: Rexp) = ALT(r, s)
+% def ~ (s: Rexp) = SEQ(r, s)
+% def % = STAR(r)
+% }
-implicit def stringOps(s: String) = new {
- def | (r: Rexp) = ALT(s, r)
- def | (r: String) = ALT(s, r)
- def ~ (r: Rexp) = SEQ(s, r)
- def ~ (r: String) = SEQ(s, r)
- def % = STAR(s)
-}
-\end{lstlisting}
+% implicit def stringOps(s: String) = new {
+% def | (r: Rexp) = ALT(s, r)
+% def | (r: String) = ALT(s, r)
+% def ~ (r: Rexp) = SEQ(s, r)
+% def ~ (r: String) = SEQ(s, r)
+% def % = STAR(s)
+% }
+% \end{lstlisting}
-\noindent This might seem a bit overly complicated, but its effect is
-that I can now write regular expressions such as $ab + ac$
-simply as
+% \noindent This might seem a bit overly complicated, but its effect is
+% that I can now write regular expressions such as $ab + ac$
+% simply as
-\begin{lstlisting}[numbers=none]
-scala> "ab" | "ac"
-res10 = ALT(SEQ(CHAR(a),CHAR(b)),SEQ(CHAR(a),CHAR(c)))
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% scala> "ab" | "ac"
+% res10 = ALT(SEQ(CHAR(a),CHAR(b)),SEQ(CHAR(a),CHAR(c)))
+% \end{lstlisting}
-\noindent I leave you to figure out what the other
-syntactic sugar in the code above stands for.
+% \noindent I leave you to figure out what the other
+% syntactic sugar in the code above stands for.
-One more useful feature of Scala is the ability to define
-functions with varying argument lists. This is a feature that
-is already present in old languages, like C, but seems to have
-been forgotten in the meantime---Java does not have it. In the
-context of regular expressions this feature comes in handy:
-Say you are fed up with writing many alternatives as
+% One more useful feature of Scala is the ability to define
+% functions with varying argument lists. This is a feature that
+% is already present in old languages, like C, but seems to have
+% been forgotten in the meantime---Java does not have it. In the
+% context of regular expressions this feature comes in handy:
+% Say you are fed up with writing many alternatives as
-\begin{lstlisting}[numbers=none]
-ALT(..., ALT(..., ALT(..., ...)))
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% ALT(..., ALT(..., ALT(..., ...)))
+% \end{lstlisting}
-\noindent To make it difficult, you do not know how deep such
-alternatives are nested. So you need something flexible that
-can take as many alternatives as needed. In Scala one can
-achieve this by adding a \code{*} to the type of an argument.
-Consider the code
+% \noindent To make it difficult, you do not know how deep such
+% alternatives are nested. So you need something flexible that
+% can take as many alternatives as needed. In Scala one can
+% achieve this by adding a \code{*} to the type of an argument.
+% Consider the code
-\begin{lstlisting}[language=Scala]
-def Alts(rs: List[Rexp]) : Rexp = rs match {
- case Nil => NULL
- case r::Nil => r
- case r::rs => ALT(r, Alts(rs))
-}
+% \begin{lstlisting}[language=Scala]
+% def Alts(rs: List[Rexp]) : Rexp = rs match {
+% case Nil => NULL
+% case r::Nil => r
+% case r::rs => ALT(r, Alts(rs))
+% }
-def ALTS(rs: Rexp*) = Alts(rs.toList)
-\end{lstlisting}
+% def ALTS(rs: Rexp*) = Alts(rs.toList)
+% \end{lstlisting}
-\noindent The function in Lines 1 to 5 takes a list of regular
-expressions and converts it into an appropriate alternative
-regular expression. In Line 7 there is a wrapper for this
-function which uses the feature of varying argument lists. The
-effect of this code is that I can write the regular
-expression for keywords as
+% \noindent The function in Lines 1 to 5 takes a list of regular
+% expressions and converts it into an appropriate alternative
+% regular expression. In Line 7 there is a wrapper for this
+% function which uses the feature of varying argument lists. The
+% effect of this code is that I can write the regular
+% expression for keywords as
-\begin{lstlisting}[numbers=none]
-ALTS("for", "def", "yield", "implicit", "if", "match", "case")
-\end{lstlisting}
+% \begin{lstlisting}[numbers=none]
+% ALTS("for", "def", "yield", "implicit", "if", "match", "case")
+% \end{lstlisting}
-\noindent Again I leave it to you to find out how much this
-simplifies the regular expression in comparison with if I had
-to write this by hand using only the ``plain'' regular
-expressions from the inductive datatype.
+% \noindent Again I leave it to you to find out how much this
+% simplifies the regular expression in comparison with if I had
+% to write this by hand using only the ``plain'' regular
+% expressions from the inductive datatype.
+
+\bigskip\noindent
+\textit{More TBD.}
\subsection*{More Info}