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+## Copyright (C) 2009 Søren Hauberg
+##
+## This program is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## This program is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Command} lookfor @var{str}
+## @deftypefnx {Command} lookfor -all @var{str}
+## @deftypefnx {Function} {[@var{fun}, @var{helpstring}] = } lookfor (@var{str})
+## @deftypefnx {Function} {[@var{fun}, @var{helpstring}] = } lookfor ('-all', @var{str})
+## Search for the string @var{str} in all of the functions found in the
+## function search path.  By default @code{lookfor} searches for @var{str}
+## in the first sentence of the help string of each function found. The entire
+## help string of each function found in the path can be searched if
+## the '-all' argument is supplied. All searches are case insensitive.
+## 
+## Called with no output arguments, @code{lookfor} prints the list of matching
+## functions to the terminal. Otherwise the output arguments @var{fun} and
+## @var{helpstring} define the matching functions and the first sentence of
+## each of their help strings.
+## 
+## Note that the ability of @code{lookfor} to correctly identify the first
+## sentence of the help of the functions is dependent on the format of the
+## functions help. All of the functions in Octave itself will correctly
+## find the first sentence, but the same can not be guaranteed for other
+## functions. Therefore the use of the '-all' argument might be necessary
+## to find related functions that are not part of Octave.
+## @seealso{help, which}
+## @end deftypefn
+
+## PKG_ADD: mark_as_command lookfor
+
+function [out_fun, out_help_text] = lookfor (str, extra)
+  if (strcmpi (str, "-all"))
+    ## The difference between using '-all' and not, is which part of the caches
+    ## we search. The cache is organised such that its first column contains
+    ## the function name, its second column contains the full help text, and its
+    ## third column contains the first sentence of the help text.
+    str = extra;
+    search_type = 2; # when using caches, search its second column
+  else
+    search_type = 3; # when using caches, search its third column
+  endif
+  str = lower (str);
+
+  ## Search operators, keywords, and built-ins
+  cache_file = fullfile (octave_config_info.datadir, "builtin_cache.mat");
+  if (exist (cache_file, "file"))
+    [fun, help_text] = search_cache (str, cache_file, search_type);
+  else
+    fun = help_text = {};
+  endif
+  
+  ## Search functions in path
+  p = path ();
+  idx = find (p == pathsep ());
+  prev_idx = 1;
+  for n = 1:length (idx)
+    f = p (prev_idx:idx (n)-1);
+    cache_file = fullfile (f, "help_cache.mat");
+    if (exist (cache_file, "file"))
+      ## We have a cache. Read it and search it!
+      [funs, hts] = search_cache (str, cache_file, search_type);
+      fun (end+1:end+length (funs)) = funs;
+      help_text (end+1:end+length (hts)) = hts;
+    else
+      ## We don't have a cache. Search files
+      funs_in_f = __list_functions__ (f);
+      for m = 1:length (funs_in_f)
+        fn = funs_in_f {m};
+        
+        ## Skip files that start with __
+        if (length (fn) > 2 && strcmp (fn (1:2), "__"))
+          continue;
+        endif
+        
+        ## Extract first sentence
+        try
+          first_sentence = get_first_help_sentence (fn);
+          status = 0;
+        catch
+          status = 1;
+        end_try_catch
+
+        if (search_type == 2) # search entire help text
+          [text, format] = get_help_text (fn);
+    
+          ## Take action depending on help text format
+          switch (lower (format))
+            case "plain text"
+              status = 0;
+            case "texinfo"
+              [text, status] = makeinfo (text, "plain text");
+            case "html"
+              [text, status] = strip_html_tags (text);
+            otherwise
+              status = 1;
+          endswitch
+
+        elseif (status == 0) # only search the first sentence of the help text
+          text = first_sentence;
+        endif
+        
+        ## Search the help text, if we can
+        if (status == 0 && !isempty (strfind (text, str)))
+          fun (end+1) = fn;
+          help_text (end+1) = first_sentence;
+        endif
+      endfor
+    endif
+    prev_idx = idx (n) + 1;
+  endfor
+  
+  if (nargout == 0)
+    ## Print the results (FIXME: improve this to make it look better.
+    indent = 20;
+    term_width = terminal_size() (2);
+    desc_width = term_width - indent - 2;
+    indent_space = repmat (" ", 1, indent);
+    for k = 1:length (fun)
+      f = fun {k};
+      f (end+1:indent) = " ";
+      printf (f);
+      desc = strtrim (strrep (help_text {k}, "\n", " "));
+      ldesc = length (desc);
+      printf ("%s\n", desc (1:min (desc_width, ldesc)));
+      for start = desc_width+1:desc_width:ldesc
+        stop = min (start + desc_width, ldesc);
+        printf ("%s%s\n", indent_space, strtrim (desc (start:stop)));
+      endfor
+    endfor
+
+  else
+    ## Return the results instead of displaying them
+    out_fun = fun;
+    out_help_text = help_text;
+  endif
+endfunction
+
+function [funs, help_texts] = search_cache (str, cache_file, search_type)
+  load (cache_file);
+  if (! isempty(cache))
+    tmp = strfind (cache (search_type, :), str);
+    cache_idx = find (!cellfun ("isempty", tmp));
+    funs = cache (1, cache_idx);
+    help_texts = cache (3, cache_idx);
+  else
+    funs = help_texts = {};
+  endif
+endfunction
+