Doubly-linked list/Element definition: Difference between revisions

<lang rexx>/*REXX program that implements various List Manager functions. */

call sy 'initializing the list.' ; call @init

call sy 'building list: Was it a cat I saw'; call @put 'Was it a cat I saw'

call sy 'displaying list size.' ; say 'list size='@size()

call sy 'forward list' ; call @show

call sy 'backward list' ; call @show ,,-1

call sy 'showing 4th item' ; call @show 4,1

call sy 'showing 5th & 6th items' ; call @show 5,2

call sy 'adding item before item 4: black' ; call @put 'black',4

call sy 'showing list' ; call @show

call sy 'adding to tail: there, in the ...'; call @put 'there, in the shadows, stalking its prey (and next meal).'

call sy 'showing list' ; call @show

call sy 'adding to head: Oy!' ; call @put 'Oy!',0

call sy 'showing list' ; call @show

exit /*stick a fork in it, we're done.*/

/*──────────────────────────────────subroutines─────────────────────────*/

p: return word(arg(1),1)

sy: say; say left('',30) "───" arg(1) '───'; return

@hasopt: arg o; return pos(o,opt)\==0

@init: $.@=''; $.#=0; return 0

@adjust: $.@=space($.@); $.#=words($.@); return 0

@parms: arg opt

if @hasopt('k') then k=min($.#+1,max(1,p(k 1)))

if @hasopt('m') then m=p(m 1)

if @hasopt('d') then dir=p(dir 1)

return

@show: procedure expose $.; parse arg k,m,dir

if dir==-1 & k=='' then k=$.#

m=p(m $.#);

say @get(k,m,dir);

return 0

@get: procedure expose $.; arg k,m,dir,_

call @parms 'kmd'

do j=k for m by dir while j>0 & j<=$.#

_=_ subword($.@,j,1)

end /*j*/

@put: procedure expose $.; parse arg x,k

k=p(k $.#+1)

call @parms 'k'

$.@=subword($.@,1,max(0,k-1)) x subword($.@,k)

call @adjust

return 0

@del: procedure expose $.; arg k,m

call @parms 'km'

_=subword($.@,k,k-1) subword($.@,k+m)

$.@=_

call @adjust

return</lang>