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)
<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 /*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 interection (or error msg)*/
if xa=xb then do
k1=.
x1=xa
if ya=yb then $= 'points A and B are identical'
end
else do
k1=(yb-ya) / (xb-xa)
d1=ya - k1 * xa
end
if xc=xd then do
k2=.
x2=xc
if yc=yd then $= 'points C and D are identical'
end
else do
k2=(yd-yc) / (xd-xc)
d2=yc - k2 * xc
end
if $=. then do
if k1=. then if k2=. then if x1=x2 then $=@ident
else $=@paral
else do
x=x1
y=k2 * x + d2
end
else if k2=. then do
x=x2
y=k1 * x + d1
end
else if k1=k2 then if d1=d2 then $= @ident
else $= @paral
else do
x=(d2-d1) / (k1-k2)
y=k1 * x + d1
end
end
if $=. then $= 'intersection is at (' || x","y')'
info= 'a=('xa","ya') b=('xb","yb') c=('xc","yc') d=('xd","yd')'
return left(info, max(50, length(info) ) ) ' ───► ' $</lang>
- output when using the default input:
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