Logo

Programming-Idioms

This language bar is your friend. Select your favorite languages!
  • Fortran

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.
  do i=1,size(items)
    if (items(i) == "asdf") then
      found = .true.
      exit
    end if
  end do
  if (.not. found) call do_something

An alternative would be to check the value of the loop variable on exit - if it is larger than size(items), then the exit statement in the loop has not been executed.
(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