Add functional.lua which implements higher-order functions

This covers all the main higher-order functions included in WFL, except zip.
The two already implemented in ai_helper have been replaced with redirection stubs.

data/ai/lua/ai_helper.lua

@@ -1,6 +1,7 @@
 local H = wesnoth.require "helper"
 local W = H.set_wml_action_metatable {}
 local LS = wesnoth.require "location_set"
+local F = wesnoth.require "functional"
 
 -- This is a collection of Lua functions used for custom AI development.
 -- Note that this is still work in progress with significant changes occurring
@@ -457,32 +458,11 @@ end
 ----- General functionality and maths helper functions ------
 
 function ai_helper.filter(input, condition)
-    -- Equivalent of filter() function in Formula AI
-
-    local filtered_table = {}
-
-    for _,v in ipairs(input) do
-        if condition(v) then
-            table.insert(filtered_table, v)
-        end
-    end
-
-    return filtered_table
+    return F.filter(input, condition)
 end
 
 function ai_helper.choose(input, value)
-    -- Equivalent of choose() function in Formula AI
-    -- Returns element of a table with the largest @value (a function)
-    -- Also returns the max value and the index
-
-    local max_value, best_input, best_key = -9e99
-    for k,v in pairs(input) do
-        if value(v) > max_value then
-            max_value, best_input, best_key = value(v), v, k
-        end
-    end
-
-    return best_input, max_value, best_key
+    return F.choose(input, value)
 end
 
 function ai_helper.table_copy(t)

data/lua/functional.lua

@@ -0,0 +1,110 @@
+-- This file implements equivalents of various higher-order WFL functions
+
+local functional = {}
+
+function functional.filter(input, condition)
+    local filtered_table = {}
+
+    for _,v in ipairs(input) do
+        if condition(v) then
+            table.insert(filtered_table, v)
+        end
+    end
+
+    return filtered_table
+end
+
+function functional.filter_map(input, condition)
+    local filtered_table = {}
+
+    for k,v in pairs(input) do
+        if condition(k, v) then
+            filtered_table[k] = v
+        end
+    end
+
+    return filtered_table
+end
+
+function functional.find(input, condition)
+	for _,v in ipairs(input) do
+		if condition(v) then
+			return v
+		end
+	end
+end
+
+function functional.find_map(input, condition)
+	for k,v in pairs(input) do
+		if condition(k,v) then
+			return k, v
+		end
+	end
+end
+
+function functional.choose(input, value)
+    -- Equivalent of choose() function in Formula AI
+    -- Returns element of a table with the largest @value (a function)
+    -- Also returns the max value and the index
+
+    local max_value, best_input, best_key = -9e99
+    for k,v in ipairs(input) do
+		local v2 = value(v)
+        if v2 > max_value then
+            max_value, best_input, best_key = v2, v, k
+        end
+    end
+
+    return best_input, max_value, best_key
+end
+
+function functional.choose_map(input, value)
+    -- Equivalent of choose() function in Formula AI
+    -- Returns element of a table with the largest @value (a function)
+    -- Also returns the max value and the index
+
+    local max_value, best_input, best_key = -9e99
+    for k,v in pairs(input) do
+		local v2 = value(k, v)
+        if v2 > max_value then
+            max_value, best_input, best_key = v2, v, k
+        end
+    end
+
+    return {key = best_key, value = best_input}, max_value
+end
+
+function functional.map(input, formula)
+	local mapped_table = {}
+	for k,v in pairs(input) do
+		if type(k) == 'number' then
+			table.insert(mapped_table, formula(v))
+		else
+			mapped_table[k] = formula(v, k)
+		end
+	end
+	return mapped_table
+end
+
+function functional.reduce(input, operator, identity)
+	if #input == 0 then return identity end
+	local value = operator(identity or 0, input[1])
+	if #input == 1 then return value end
+	for i = 2, #input do
+		value = operator(value, input[i])
+	end
+	return value
+end
+
+function functional.take_while(input, condition)
+	local truncated_table = {}
+	for _,v in ipairs(input) do
+		if not condition(v) then
+			break
+		end
+		table.insert(truncated_table, v)
+	end
+	return truncated_table
+end
+
+return functional