Use the following example source code:

module test_mod
  implicit none

contains

  subroutine a()
  end subroutine a

  subroutine b()
  end subroutine b

  subroutine c()
  end subroutine c

  subroutine d()
  end subroutine d

end module test_mod

enable hide-show-mode (hs-minor-mode) and execute command
hs-hide-level when cursor is outside of any subroutine. The result is that
only every other subroutine gets hidden.
This can be also reproduced with emacs 23.2.1 (debian-stable).


In GNU Emacs 24.0.95.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.20.1)
 of 2012-04-17 on sommerfeld
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
Configured using:
 `configure '--prefix=/home/p0friedr/a_dait01/local/emacs''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: de_DE.utf8
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: F90

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t
  hs-minor-mode: t

Recent input:
C-x C-f p r o j <tab> <down-mouse-1> <mouse-1> <down-mouse-1>
<mouse-1> h i <tab> <backspace> <backspace> C-g C-x
C-f t m p . f 9 0 <return> i <backspace> m o d u l
e SPC t e s t _ m o d <return> i <backspace> <tab>
i m p l i c i t SPC n o n e <return> <return> <tab>
c o n t a i n s <return> <up> <tab> <down> i <tab>
<backspace> <help-echo> <down-mouse-1> <mouse-1> <return>
<tab> s u b r o u t i n e SPC a ( ) <return> <return>
e n d <tab> <down> <return> <return> s u r <backspace>
b r o u t i n e SPC b ( ) <return> e n d <tab> <up>
<tab> <down> <tab> <down> <return> <up> <up> <up> <up>
<up> d d <escape> <backspace> <backspace> <down> <down>
<down> <down> <end> <return> <return> <tab> s u b r
o u t i n e SPC c ( ) <return> e n d <tab> <end> <return>
<return> s u r <backspace> <tab> b r o u t i n e SPC
d ( ) <return> e n d <tab> <return> <escape> u <escape>
u <backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> <backspace>
<backspace> <backspace> <backspace> <backspace> <tab>
<end> <return> <return> e n d <tab> M-x h s - m i n
o <tab> <return> <up> <up> <up> <up> <up> <up> <up>
<up> <up> <up> <up> <up> <up> M-x h s - h i <tab> l
<tab> <return> <up> <up> <up> <up> <left> <left> C-SPC
<down> <down> <down> <down> <down> <down> <down> <down>
<down> <down> <down> <down> <down> <down> <down> <end>
C-w C-y <escape> M-x M-x r e p o <tab> <help-echo>
<help-echo> <down-mouse-1> <mouse-2>

Recent messages:
Inserting d.
Inserting subroutine.
Inserting d.
Inserting module.
Inserting test_mod.
Hs minor mode enabled
Hiding blocks ... done
You can run the command `hs-hide-level' with C-c @ C-l
Mark set [2 times]
Making completion list...

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail regexp-opt rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils help-mode view hideshow vc-dispatcher
vc-svn f90 cus-edit easymenu cus-start cus-load wid-edit time-date
tooltip ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
dnd fontset image fringe lisp-mode register page menu-bar rfn-eshadow
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core frame cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer loaddefs button faces
cus-face files text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget hashtable-print-readable backquote
make-network-process dbusbind dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)