Talk:Find the intersection of two lines

a REXX version of a REXX version

This REXX version is a re-write of version 2 of the REXX entry, with:

•   aligned indentation for all   do-end   blocks   (and encapsulated statements)
•   elided superfluous zeroes and decimal points in (decimal) integers
•   elides the superfluous and detracting use of concatenation   (││)
•   a unique symbol instead of a null literal for a special case
•   aligns the data points and results in the output
•   adds whitespace to make arithmetic computations more perusable
•   eschews title-case capitalization
•   maintains the same line for the   then   clause and the   if   clause   (no split statements)
•   indentations for all REXX statements in the function
•   has the result on the same line as the input   (data points)
•   a different quoted literal style   (for easier reading of multiple literals on the same clause)
•   REXX variables to hold long literals that would otherwise cause excessive wide REXX statements
•   a comma   (instead of a slash)   to separate the   x   y   coördinates of the data points.
•   elides superfluous   do-end   block structures
•   a lot more whitespace within REXX statements and the REXX program's output
•   tests all data possibilities   (for showing all the tested non-intersecting conditions)

Translation of: REXX (version 2)

<lang rexx>/*REXX program finds (possibly) the intersection of two lines (with diagnostic errors).*/ say iSect( 4 0 6 10 0 3 10 7 ) say iSect( 0 0 0 10 0 3 10 7 ) say iSect( 0 0 0 10 0 3 10 7 ) say iSect( 0 0 0 1 1 0 1 7 ) say iSect( 0 0 0 0 0 3 10 7 ) say iSect( 0 0 3 3 0 0 6 6 ) say iSect( 0 0 3 3 0 1 6 7 ) say iSect( 0 0 3 3 8 8 8 8 ) exit /* ═══a═══ ═══b═══ ═══c═══ ═══c═══ stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ iSect: procedure; parse arg xa ya xb yb xc yc xd yd

      @ident= 'lines  AB  and  CD  are identical'      /*literal to help shorten a line*/
      @paral= 'lines  AB  and  CD  are  parallel'      /*   "     "   "     "    "   " */
      $=.                                              /*the intersection or error msg.*/
      if xa=xb  then do                                /*is  AB  a vertical line?      */
                     k1=.                              /*the slope is infinite.        */
                     x1=xa                             /*the  X's  intersection is  XA */
                     if ya=yb  then $= 'points  A  and  B   are identical'
                     end
                else do                                /*AB  isn't a vertical line.    */
                     k1=(yb-ya) / (xb-xa)              /*compute the slope of  AB      */
                     d1=ya - k1 * xa                   /*calc. intersection with Y axis*/
                     end

      if xc=xd  then do                                /*is  CD  a vertical line?      */
                     k2=.                              /*the slope is infinite.        */
                     x2=xc                             /*the  C's  intersection is  XC */
                     if yc=yd  then $= 'points  C  and  D   are identical'
                     end
                else do                                /*CD  isn't a vertical line.    */
                     k2=(yd-yc) / (xd-xc)              /*compute the slope of  CD      */
                     d2=yc - k2 * xc                   /*calc. intersection with Y axis*/
                     end

      if $=.  then do                                  /*no special case so far ···    */
                   if k1=. then  if k2=. then  if x1=x2  then  $=@ident   /*identical. */
                                                         else  $=@paral   /*parallel.  */
                                         else  do
                                               x=x1                       /*use  X1    */
                                               y=k2 * x + d2              /*Y from CD  */
                                               end
                           else  if k2=. then  do                         /*vertical CD*/
                                               x=x2                       /*X from CD  */
                                               y=k1 * x + d1              /*Y from AB  */
                                               end
                                         else  if k1=k2  then  if d1=d2  then $= @ident
                                                                         else $= @paral
                                                         else  do             /*normal.*/
                                                               x=(d2-d1) / (k1-k2)
                                                               y=k1 * x + d1
                                                               end        /*normal line*/
                   end

      if $=.  then $= 'intersection is at  (' || x","y')'                 /*$ ¬defined?*/
      info=left( 'a=('xa","ya')', 12)     left( 'b=('xb","yb')', 12),
           left( 'c=('xc","yc')', 12)     left( 'd=('xd","yd')', 12)
      return left(info, max(51, length(info) ) )          ' ───► '     $  /*return str.*/</lang>

output   when using the default inputs:

a=(4,0)      b=(6,10)     c=(0,3)      d=(10,7)      ───►  intersection is at  (5,5)
a=(0,0)      b=(0,10)     c=(0,3)      d=(10,7)      ───►  intersection is at  (0,3)
a=(0,0)      b=(0,10)     c=(0,3)      d=(10,7)      ───►  intersection is at  (0,3)
a=(0,0)      b=(0,1)      c=(1,0)      d=(1,7)       ───►  lines  AB  and  CD  are  parallel
a=(0,0)      b=(0,0)      c=(0,3)      d=(10,7)      ───►  points  A  and  B   are identical
a=(0,0)      b=(3,3)      c=(0,0)      d=(6,6)       ───►  lines  AB  and  CD  are identical
a=(0,0)      b=(3,3)      c=(0,1)      d=(6,7)       ───►  lines  AB  and  CD  are  parallel
a=(0,0)      b=(3,3)      c=(8,8)      d=(8,8)       ───►  points  C  and  D   are identical

==================================================================================

If I were to translate many of the Rexx programs of GS to my liking I'd be busy for months.

•  Here is the Rexx program as I wrote it in my style:::*  

http://rosettacode.org/wiki/Find_the_intersection_of_two_lines#version_2

•  Any opinions from any peers? --Walterpachl (talk) 06:01, 19 May 2017 (UTC)

---

There is no reason to take it personally.   It wasn't meant as a criticism, it is just another version in a different style, albeit a fair number of (style) differences.   Everybody's code can be improved (as least, the style can be changed).   In this case, I elided a few superfluous statements, which, in my opinion, didn't add anything to the REXX program or make it easier to understand/peruse.   I didn't appreciate your style of capitalization, misaligned DO-END statements (and the intervening/encapsulating REXX statements), split IF-THEN clauses, and much more.     But, that's only my opinion and preferences,   I merely added a version that I found easier to read and understand (and I hoped others will appreciate this version), and I also removed superfluous DO-END blocks and such.   Note that this re-written REXX version was added in the   discussion   section, not on the   page   section so as to not clutter up the main page.   I found that that particular REXX version was so difficult to follow and understand (the IF logic) with all the multiple misaligned DO-END and compound IF THEN-ELSE statements.   The version (above) that I re-wrote speaks to style and understandability.   There are many styles to write REXX programs in, and this is just one of them.   Nobody's style is everybody's cup of tea.   -- Gerard Schildberger (talk) 08:22, 19 May 2017 (UTC)

---

The only thing I liked about this variation is the presentation of the result.

The a= etc. should be A= etc. to be consistent.

I dislike that the variation can no longer be used with ooRexx :-(

and i cannot appreciate the landscape formatting!

But let's agree that our taste as far as formatting is concerned is vastly different.

And I added commentary to my version. --Walterpachl (talk) 09:29, 19 May 2017 (UTC)