Ansification of chapter 7 (except DOER/MAKE)

coordinates in this order:

\begin{Code}

( x1 y1 x2 y2)

( x1 y1 x2 y2 -- )

\end{Code}

where $x_1,y_1$ represent the $x,y$ coordinates for the one end-point, and

$x_2,y_2$ represent the opposite end-point.

takes four arguments in this order:

\begin{Code}

( x1 y1 x2 y2)

( x1 y1 x2 y2 -- )

\end{Code}

where x1 y1 represent the $x,y$ coordinates for the upper left-hand corner

of the box, and x2 y2 represent the lower right-hand corner coordinates.

part of the design.

\begin{interview}

\person{Bernd Paysan}:

\person{Paysan}:

\begin{tfquot}

I prefer turtle graphics. This is a turtle graphics without cursor

same situation comes up more than once, apply a technique of factoring:

\begin{Code}

: bury  ( a -- )  dup 2+  2 cmove ;

: exhume  ( a -- )  dup 2+  swap 2 cmove ;

: bury  ( a -- )  dup cell+  1 cells  move ;

: exhume  ( a -- )  dup cell+  swap 1 cells  move ;

\end{Code}

Then instead of defining two variables, such as \forth{CONDITION} and

\forth{OLD-CONDITION}, define one double-length variable:

: diddle    condition bury  17 condition !  ( diddle )

   condition exhume ;

\end{Code}

\forth{BURY} saves the ``old'' version of condition at \forth{CONDITION 2+}.

\forth{BURY} saves the ``old'' version of condition at \forth{CONDITION CELL+}.

You still have to be careful. Going back to our \forthb{DUMP} example,

suppose you decided to add the friendly feature of letting the user exit

\begin{center}

\begin{BVerbatim}

0 Value pointers  \ address of state table patched later

: Position   ( o -- o+2 ) Create dup ,  2+

: Position   ( o -- o+cell ) Create dup ,  cell+

   DOES>  ( -- a )  @  pointers + ;

0  \ initial offset

Position top

\begin{BVerbatim}

Variable 'pointers  \ pointer to state table

: pointers ( -- adr-of-current-table )   'pointers @ ;

: Position   ( o -- o+2 ) Create dup ,  2+

: Position   ( o -- o+cell ) Create dup ,  cell+

   DOES>  ( -- a )  @ pointers + ;

0  \ initial offset

Position top