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Programming-Idioms

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  • Pascal

Idiom #223 for else loop

Loop through list items checking a condition. Do something else if no matches are found.

A typical use case is looping through a series of containers looking for one that matches a condition. If found, an item is inserted; otherwise, a new container is created.

These are mostly used as an inner nested loop, and in a location where refactoring inner logic into a separate function reduces clarity.

Found := False;
for Item in Items do
begin
  if Item.MatchesCondition then
  begin
    Found := True;
    Break;
  end;
end;
if not Found then 
  DoSomethingElse;
(if (seq (filter odd? my-col))
  "contains odds"
  "no odds found")

(seq (filter pred-fn col)) returns nil when there are no matches, and nil is falsy.

New implementation...
< >
Ruien