Valid function

README.md

@@ -18,6 +18,7 @@ A library for Lua to validate various values and table structures.
   - [`valid.arrayof`](#validarrayof)
   - [`valid.map`](#validmap)
   - [`valid.mapof`](#validmapof)
+  - [`valid.func`](#validfunc)
 - [Error Handling and Invalid Propagation](#error-handling-and-invalid-propagation)
 - [Contributing](#contributing)
 - [License](#license)
@@ -384,6 +385,28 @@ assert(not is_valid)  -- false, "name" is required for "bob"
     * `empty`:  Set to `true` to allow empty maps.
     * `func`: A table containing two custom validation functions, one for the keys and one for the values.
 
+### `valid.func`
+
+Validates that a value is a function.
+
+#### Usage
+
+```lua
+local valid = require "valid"
+
+local valid_function = valid.func()
+
+local is_valid = valid_function(function() end)
+assert(is_valid) -- true
+
+local is_valid = valid_function("123")
+assert(not is_valid) -- false, not a function
+```
+
+#### Parameters
+
+*(none)*
+
 ## Error Handling and Invalid Propagation
 
 The library provides detailed error information when validation fails. When `is_valid` is `false`, additional values are provided to help identify the nature of the validation failure:

tests.lua

@@ -74,7 +74,35 @@ describe("Validation Library Tests", function()
         }
     }
 
+    local simple_function = function() end
+
     local tests = {
+        -- Valid simple function
+        {
+            description = "Valid simple function",
+            definition = valid.func(),
+            data = simple_function,
+            expected = {
+                is_valid = true,
+                val_or_err = simple_function,
+                badval_or_nil = nil,
+                path_or_nil = nil
+            }
+        },
+
+        -- Invalid function
+        {
+            description = "Invalid function",
+            definition = valid.func(),
+            data = "123",
+            expected = {
+                is_valid = false,
+                val_or_err = "func",
+                badval_or_nil = "123",
+                path_or_nil = nil
+            }
+        },
+
         -- Valid contact data
         {
             description = "Valid contact data",

valid.lua

@@ -339,4 +339,15 @@ local function mapof(deffuncs, opts)
 end
 _M.mapof = mapof
 
+local function func()
+    return function(val)
+        if type(val) ~= "function" then
+            return false, "func", val
+        end
+
+        return true, val
+    end
+end
+_M.func = func
+
 return _M