vim: factor out reusable functions into a separate module

config/nvim/lua/user/plugins/completion.lua

@@ -1,11 +1,8 @@
 local config = function()
   local cmp = require('cmp')
 
-  -- flip(f)(a, b) == f(b, a)
-  local flip = function(f) return function(a, b) return f(b, a) end end
-
-  -- partial(f, x)(...) == f(x, ...)
-  local partial = function(f, x) return function(...) return f(x, ...) end end
+  local partial = require('user.util').partial
+  local flip    = require('user.util').flip
 
   -- assign('i',        { key = func, ... }) == { key = { i = func }, ... }
   -- assign({'i', 'c'}, { key = func, ... }) == { key = { i = func, c = func }, ...}

config/nvim/lua/user/plugins/telescope.lua

@@ -103,21 +103,7 @@ local config = function()
   telescope.load_extension 'file_browser'
   telescope.load_extension 'fzf'
 
-  local with_saved_register = function(register, func)
-    local saved = vim.fn.getreg(register)
-    local result = func()
-    vim.fn.setreg(register, saved)
-    return result
-  end
-
-  local get_selected_text = function()
-    if vim.fn.mode() ~= 'v' then return vim.fn.expand '<cword>' end
-
-    return with_saved_register('v', function()
-      vim.cmd [[noautocmd sil norm "vy]]
-      return vim.fn.getreg 'v'
-    end)
-  end
+  local get_selected_text = require('user.util').get_selected_text
 
   local custom = {
     all_files = function()

config/nvim/lua/user/util.lua

@@ -0,0 +1,43 @@
+local M = {}
+
+-- Flip function arguments.
+--
+--    flip(f)(a, b) == f(b, a)
+--
+M.flip = function(f)
+  return function(a, b)
+    return f(b, a)
+  end
+end
+
+-- Partial function application:
+--
+--    partial(f, x)(...) == f(x, ...)
+--
+M.partial = function(f, x)
+  return function(...)
+    return f(x, ...)
+  end
+end
+
+-- Perform `func` (which can freely use register `reg`) and make sure `reg`
+-- is restored afterwards.
+M.with_saved_register = function(reg, func)
+  local saved = vim.fn.getreg(reg)
+  local result = func()
+  vim.fn.setreg(reg, saved)
+  return result
+end
+
+-- Get selected text, or word under cursor if not in visual mode.
+M.get_selected_text = function()
+  if vim.fn.mode() ~= 'v' then return vim.fn.expand '<cword>' end
+
+  return M.with_saved_register('v', function()
+    vim.cmd [[noautocmd sil norm "vy]]
+    return vim.fn.getreg 'v'
+  end)
+end
+
+return M
+