convert mode/paste/iminsert parts to function names.

autoload/airline/parts.vim

@@ -1,13 +1,31 @@
 " MIT License. Copyright (c) 2013 Bailey Ling.
 " vim: et ts=2 sts=2 sw=2
 
+function! airline#parts#append(name)
+  let val = function(a:name)()
+  return empty(val) ? '' : '  '.g:airline_left_alt_sep.' '.val
+endfunction
+
+function! airline#parts#prepend(name)
+  let val = function(a:name)()
+  return empty(val) ? '' : val.' '.g:airline_right_alt_sep
+endfunction
+
+function! airline#parts#empty()
+  return ''
+endfunction
+
+function! airline#parts#mode()
+  return get(w:, 'airline_current_mode', '')
+endfunction
+
 function! airline#parts#paste()
-  return g:airline_detect_paste && &paste ? '  '.g:airline_symbols.paste : ''
+  return g:airline_detect_paste && &paste ? g:airline_symbols.paste : ''
 endfunction
 
 function! airline#parts#iminsert()
   if g:airline_detect_iminsert && &iminsert && exists('b:keymap_name')
-    return '  '.g:airline_left_alt_sep.' '.toupper(b:keymap_name)
+    return toupper(b:keymap_name)
   endif
   return ''
 endfunction

autoload/airline/util.vim

@@ -1,6 +1,24 @@
 " MIT License. Copyright (c) 2013 Bailey Ling.
 " vim: et ts=2 sts=2 sw=2
 
+function! s:get_val(part)
+  let val = g:airline_parts[a:part]
+  if match(val, '%') > -1
+    return val
+  else
+    return '%{function("'.val.'")()}'
+  endif
+endfunction
+
+function! airline#util#define_section(key, parts)
+  if !exists('g:airline_section_{a:key}') && len(a:parts) > 0
+    let g:airline_section_{a:key} = s:get_val(a:parts[0])
+    for i in range(1, len(a:parts) - 1)
+      let g:airline_section_{a:key} .= s:get_val(a:parts[i])
+    endfor
+  endif
+endfunction
+
 if v:version >= 704
   function! airline#util#getwinvar(winnr, key, def)
     return getwinvar(a:winnr, a:key, a:def)

plugin/airline.vim

@@ -34,7 +34,7 @@ function! s:init()
 
     call s:check_defined('g:airline_symbols', {})
     call extend(g:airline_symbols, {
-          \ 'paste': get(g:, 'airline_paste_symbol', g:airline_left_alt_sep.' PASTE'),
+          \ 'paste': get(g:, 'airline_paste_symbol', 'PASTE'),
           \ 'readonly': get(g:, 'airline_readonly_symbol', get(g:, 'airline_powerline_fonts', 0) ? '' : 'RO'),
           \ 'whitespace': get(g:, 'airline_powerline_fonts', 0) ? '✹' : '!',
           \ 'linenr': get(g:, 'airline_linecolumn_prefix', get(g:, 'airline_powerline_fonts', 0) ? '' : ':' ),
@@ -43,17 +43,17 @@ function! s:init()
 
     call s:check_defined('g:airline_parts', {})
     call extend(g:airline_parts, {
-          \ 'mode': '%{get(w:,"airline_current_mode","")}',
-          \ 'iminsert': '%{airline#parts#iminsert()}',
-          \ 'paste': '%{airline#parts#paste()}',
+          \ 'mode': 'airline#parts#mode',
+          \ 'iminsert': 'airline#parts#iminsert',
+          \ 'paste': 'airline#parts#paste',
           \ 'readonly': '%#airline_file#%{airline#parts#readonly()}',
           \ 'ffenc': '%{printf("%s%s",&fenc,strlen(&ff)>0?"[".&ff."]":"")}',
           \ 'file': '%f%m',
-          \ 'hunks': '',
-          \ 'branch': '',
-          \ 'tagbar': '',
-          \ 'syntastic': '',
-          \ 'whitespace': '',
+          \ 'hunks': 'airline#parts#empty',
+          \ 'branch': 'airline#parts#empty',
+          \ 'tagbar': 'airline#parts#empty',
+          \ 'syntastic': 'airline#parts#empty',
+          \ 'whitespace': 'airline#parts#empty',
           \ }, 'keep')
 
     call s:check_defined('g:airline_mode_map', {})
@@ -80,7 +80,7 @@ function! s:init()
           \ }, 'keep')
 
     call airline#extensions#load()
-    call s:check_defined('g:airline_section_a', (g:airline_parts.mode).(g:airline_parts.paste).(g:airline_parts.iminsert))
+    call airline#util#define_section('a', ['mode', 'paste', 'iminsert'])
     call s:check_defined('g:airline_section_b', (g:airline_parts.hunks).(g:airline_parts.branch))
     call s:check_defined('g:airline_section_c', '%<'.(g:airline_parts.file))
     call s:check_defined('g:airline_section_gutter', ' '.(g:airline_parts.readonly).'%=')