1 files changed, 87 insertions, 0 deletions
diff --git a/lib/lyaml/functional.lua b/lib/lyaml/functional.lua
new file mode 100644
index 000000000000..556e9489505a
--- /dev/null
+++ b/lib/lyaml/functional.lua
@@ -0,0 +1,87 @@
+-- Minimal functional programming utilities.
+-- Written by Gary V. Vaughan, 2015
+--
+-- Copyright(C) 2015-2022 Gary V. Vaughan
+--
+-- Permission is hereby granted, free of charge, to any person obtaining
+-- a copy of this software and associated documentation files(the
+-- "Software"), to deal in the Software without restriction, including
+-- without limitation the rights to use, copy, modify, merge, publish,
+-- distribute, sublicense, and/or sell copies of the Software, and to
+-- permit persons to whom the Software is furnished to do so, subject to
+-- the following conditions:
+--
+-- The above copyright notice and this permission notice shall be
+-- included in all copies or substantial portions of the Software.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+-- EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+-- MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+-- IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+-- CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+-- TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+-- SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+--- @module lyaml.functional
+
+
+--- `lyaml.null` value.
+-- @table NULL
+local NULL = setmetatable({}, {_type='LYAML null'})
+
+
+--- `lyaml.null` predicate.
+-- @param x operand
+-- @treturn bool `true` if *x* is `lyaml.null`.
+local function isnull(x)
+   return(getmetatable(x) or {})._type == 'LYAML null'
+end
+
+
+--- Callable predicate.
+-- @param x operand
+-- @treturn bool `true` if *x* is a function has a __call metamethod
+-- @usage r = iscallable(x) and x(...)
+local function iscallable(x)
+   if type(x) ~= 'function' then
+      x =(getmetatable(x) or {}).__call
+   end
+   if type(x) == 'function' then
+      return x
+   end
+end
+
+
+--- Compose a function to try each callable with supplied args.
+-- @tparam table fns list of functions to try
+-- @treturn function a new function to call *...* functions, stopping
+--    and returning the first non-nil result, if any
+local function anyof(fns)
+   return function(...)
+      for _, fn in ipairs(fns) do
+         if iscallable(fn) then
+            local r = fn(...)
+            if r ~= nil then
+               return r
+            end
+         end
+      end
+   end
+end
+
+
+--- Return arguments unchanged.
+-- @param ... arguments
+-- @return *...*
+local function id(...)
+   return ...
+end
+
+--- @export
+return {
+   NULL = NULL,
+   anyof = anyof,
+   id = id,
+   iscallable = iscallable,
+   isnull = isnull,
+}