40 % 10 MOST(LY DEAD) INFLUENTIAL PROGRAMMING LANGUAGES

    40 % 10 MOST(LY DEAD) INFLUENTIAL PROGRAMMING LANGUAGES

    41 % https://www.hillelwayne.com/post/influential-dead-languages/

    41 % https://www.hillelwayne.com/post/influential-dead-languages/

    42 

    42 

    43 

    43 

    44 \begin{document}

    44 \begin{document}

    46 

    46 

    47 \section*{Handout 1}

    47 \section*{Handout 1}

    48 

    48 

    49 

    49 

    50 The purpose of a compiler is to transform a program a human can read and

    50 The purpose of a compiler is to transform a program a human can read and

    52 compiler is an old craft going back to 1952 with the first compiler

    52 compiler is an old craft going back to 1952 with the first compiler

    53 written by Grace Hopper.\footnote{Who many years ago was invited on a

    53 written by Grace Hopper.\footnote{Who many years ago was invited on a

    54 talk show hosted by David Letterman.

    54 talk show hosted by David Letterman.

    55 \here{https://youtu.be/3N_ywhx6_K0?t=31}} Why studying compilers

    55 \here{https://youtu.be/3N_ywhx6_K0?t=31}} Why studying compilers

    56 nowadays?  An interesting answer is given by John Regher in his compiler

    56 nowadays?  An interesting answer is given by John Regher in his compiler

   342 \url{https://www.tutorialdocs.com/article/regex-trap.html}

   342 \url{https://www.tutorialdocs.com/article/regex-trap.html}

   343 \end{center}  

   343 \end{center}  

   344 

   344 

   345 \noindent

   345 \noindent

   346 Finally, on 2 July 2019 Cloudflare had a global outage because of a 

   346 Finally, on 2 July 2019 Cloudflare had a global outage because of a 

   348 happened is nicely explained in the blog:

   348 happened is nicely explained in the blog:

   349 

   349 

   350 \begin{center}

   350 \begin{center}

   351 \url{https://blog.cloudflare.com/details-of-the-cloudflare-outage-on-july-2-2019}

   351 \url{https://blog.cloudflare.com/details-of-the-cloudflare-outage-on-july-2-2019}

   352 \end{center}  

   352 \end{center}  

   529 but often just write {\it hello}.

   529 but often just write {\it hello}.

   530 

   530 

   531 If you prefer to think in terms of the implementation

   531 If you prefer to think in terms of the implementation

   532 of regular expressions in Scala, the constructors and

   532 of regular expressions in Scala, the constructors and

   533 classes relate as follows\footnote{More about Scala is 

   533 classes relate as follows\footnote{More about Scala is 

   535 

   535 

   536 \begin{center}

   536 \begin{center}

   537 \begin{tabular}{rcl}

   537 \begin{tabular}{rcl}

   538 $\ZERO$       & $\mapsto$ & \texttt{ZERO}\\

   538 $\ZERO$       & $\mapsto$ & \texttt{ZERO}\\

   539 $\ONE$        & $\mapsto$ & \texttt{ONE}\\

   539 $\ONE$        & $\mapsto$ & \texttt{ONE}\\

   619                      & = & L(r_1) \cup L(r_2) \cup L(r_3)\\

   619                      & = & L(r_1) \cup L(r_2) \cup L(r_3)\\

   620                      & = & L(r_1) \cup L(r_2 + r_3)\\

   620                      & = & L(r_1) \cup L(r_2 + r_3)\\

   621                      & = & L(r_1 + (r_2 + r_3))

   621                      & = & L(r_1 + (r_2 + r_3))

   622 \end{eqnarray*}

   622 \end{eqnarray*}

   623 

   623 

   624 The point of the definition of $L$ is that we can use it to

   626 The point of the definition of $L$ is that we can use it to

   625 precisely specify when a string $s$ is matched by a regular

   627 precisely specify when a string $s$ is matched by a regular

   626 expression $r$, namely if and only if $s \in L(r)$. In fact we

   628 expression $r$, namely if and only if $s \in L(r)$. In fact we

   627 will write a program \pcode{match} that takes any string $s$

   629 will write a program \pcode{match} that takes any string $s$

   628 and any regular expression $r$ as arguments and returns

   630 and any regular expression $r$ as arguments and returns

   713 have surprised some experts. Together with two colleagues from China, I was

   715 have surprised some experts. Together with two colleagues from China, I was

   714 able to prove the Myhill-Nerode theorem by only using regular

   716 able to prove the Myhill-Nerode theorem by only using regular

   715 expressions and the notion of derivatives. Earlier versions of

   717 expressions and the notion of derivatives. Earlier versions of

   716 this theorem used always automata in the proof. Using this

   718 this theorem used always automata in the proof. Using this

   717 theorem we can show that regular languages are closed under

   719 theorem we can show that regular languages are closed under

   719 blog\footnote{\url{http://goo.gl/2R11Fw}} assumed can only be

   721 blog\footnote{\url{http://goo.gl/2R11Fw}} assumed can only be

   720 shown via automata. So even somebody who has written a 700+-page

   722 shown via automata. So even somebody who has written a 700+-page

   721 book\footnote{\url{http://goo.gl/fD0eHx}} on regular

   723 book\footnote{\url{http://goo.gl/fD0eHx}} on regular

   722 expressions did not know better. Well, we showed it can also be

   724 expressions did not know better. Well, we showed it can also be

   723 done with regular expressions only.\footnote{\url{http://nms.kcl.ac.uk/christian.urban/Publications/posix.pdf}}

   725 done with regular expressions only.\footnote{\url{http://nms.kcl.ac.uk/christian.urban/Publications/posix.pdf}}