\quad \chapterprecishere{``Begin at the beginning'', the King said gravely, ``and go on till you come to the end: then stop.''\par\raggedleft --- \textup{Lewis Carroll, } Alice in Wonderland} We'll begin at the beginning; how beginning? This: \begin{lstlisting} 10 PRINT 2+2 run 4 Ok \end{lstlisting} Oh \emph{boy} we just did a computation! It printed out \code{4} which is a correct answer for $2+2$ and it didn't crash! \section[GOTO]{GOTO here and there} \section[When GOTO Is Bad]{Severe Acute Spaghettification Syndrome} \section[Subroutine with GOSUB]{GOSUB to the rescue!} \section[FOR-NEXT Loop]{FOR ever loop NEXT} \begin{lstlisting} 10 FOR I = 1 TO 20 20 PRINT SPC(20-I); 30 FOR J = 1 TO I*2-1 40 PRINT "*"; 50 NEXT:PRINT 60 NEXT \end{lstlisting} \section[Get User INPUT]{Isn't It Nice To Have a Computer That Will Question You?} \section[Recursion]{BRB: Bad Recursion BRB: Bad Recursion BRB: Bad Recursion BRB: Bad RecursionBRB: Bad Recursion BRBRangeError: Maximum call stack size exceeded} \begin{lstlisting} 10 DEFUN ENDLESS(SHIT)=ENDLESS(SHIT) 20 ENDLESS(1) \end{lstlisting} \begin{lstlisting} 10 DEFUN FAC(N)=IF N==0 THEN 1 ELSE N*FAC(N-1) 20 FOR K=1 TO 6 30 PRINT FAC(K) 40 NEXT \end{lstlisting} \begin{lstlisting} 10 DEFUN FAC(N)=IF N==0 THEN 1 ELSE N*FAC(N-1) 20 K=MAP FAC, 1 TO 10 30 PRINT K \end{lstlisting} \begin{lstlisting} 10 DEFUN FIB(N)=IF N==0 THEN 0 ELSE IF N==1 THEN 1 ELSE FIB(N-1)+FIB(N-2) 20 FOR K=1 TO 12 30 PRINT FIB(K);" "; 40 NEXT \end{lstlisting} \section[Currying]{Haskell Curry Wants to Know Your Location} \label{currying101} So what the fsck is currying? Consider the following code: \begin{lstlisting} 10 DEFUN F(K,T)=ABS(T)==K 20 CF=F<~32 30 PRINT CF(24) : REM will print 'false' 40 PRINT CF(-32) : REM will print 'true' \end{lstlisting} % NOTE: you can't use \basiccurry within \code{} Here, \code{CF} is a curried function of \code{F}; built-in operator \code{$<\!\sim$} applies \code{32} to the first parameter of the function \code{F}, which dynamically returns a \emph{function} of \code{CF(T) = ABS(T) == 32}. The fact that Curry Operator returns a \emph{function} opens many possibilities, for example, you can create loads of sibling functions without making loads of duplicate codes. \section[Wrapping-Up]{The Grand Unification} Using all the knowledge we have learned, it should be trivial\footnote{/s} to write a Quicksort function in \tbas, like this: \begin{lstlisting} 10 DEFUN LESS(P,X)=X

=P 12 DEFUN QSORT(XS)=IF LEN(XS)<1 THEN NIL ELSE QSORT(FILTER(LESS<~HEAD(XS),TAIL(XS))) # HEAD(XS)!NIL # QSORT(FILTER(GTEQ<~HEAD(XS),TAIL(XS))) 100 L=7!9!4!5!2!3!1!8!6!NIL 110 PRINT L 120 PRINT QSORT(L) \end{lstlisting} Line 12 implements quicksort algorithm, using \code{LESS} and \code{GTEQ} as helper functions. \code{LESS} is a user-function version of less-than operator, and \code{GTEQ} is similar. \code{QSORT} selects a pivot by taking the head-element of the array \code{XS}\footnote{stands for \emph{X's}} with \code{HEAD(XS)}, then utilises curried version of \code{LESS} and \code{GTEQ} to move lesser-than-pivot values to the left and greater to the right (the head element itself does not get recursed, here \code{TAIL(XS)} is applied to make head-less copy of the array), and these two separated \emph{chunks} are recursively sorted using the same \code{QSORT} function. Currying is exploited to give comparison functions a pivot-value to compare against, and also because \code{FILTER} wants a \emph{function} and not an \emph{expression}. \code{HEAD(XS)!NIL} creates a single-element array contains head-element of the \code{XS}. %Uncomment this if you finally decided to support a closure% %% Using \emph{closure}, the definition of \code{QSORT} can truly be a one-liner and be \emph{even more cryptic}: %% %% \begin{lstlisting} %% 10 QSORT=[XS]~>IF LEN(XS)<1 THEN NIL ELSE %% QSORT(FILTER([K]~>KK>=HEAD XS,TAIL XS)) %% \end{lstlisting}