feat(functional): add list.reduce (#772)

3 files changed, 24 insertions, 0 deletions

diff --git a/lua/mason-core/functional/init.lua b/lua/mason-core/functional/init.lua
index dbb27ddd..ee185e8b 100644
--- a/lua/mason-core/functional/init.lua
+++ b/lua/mason-core/functional/init.lua
@@ -61,6 +61,7 @@ _.partition = list.partition
 _.take = list.take
 _.drop = list.drop
 _.drop_last = list.drop_last
+_.reduce = list.reduce
 
 ---@module "mason-core.functional.relation"
 local relation = lazy_require "mason-core.functional.relation"
diff --git a/lua/mason-core/functional/list.lua b/lua/mason-core/functional/list.lua
index 7c66ccac..8c216c4d 100644
--- a/lua/mason-core/functional/list.lua
+++ b/lua/mason-core/functional/list.lua
@@ -257,4 +257,16 @@ _.drop_last = fun.curryN(function(n, list)
     return result
 end, 2)
 
+---@generic T, U
+---@param fn fun(acc: U, item: T): U
+---@param acc U
+---@param list T[]
+---@return U
+_.reduce = fun.curryN(function(fn, acc, list)
+    for i = 1, #list do
+        acc = fn(acc, list[i])
+    end
+    return acc
+end, 3)
+
 return _
diff --git a/tests/mason-core/functional/list_spec.lua b/tests/mason-core/functional/list_spec.lua
index a53da4ac..7c3d8cfb 100644
--- a/tests/mason-core/functional/list_spec.lua
+++ b/tests/mason-core/functional/list_spec.lua
@@ -253,4 +253,15 @@ describe("functional: list", function()
         assert.same({ "First", "Second", "Third", "I", "Have", "Poor", "Imagination" }, _.drop_last(0, list))
         assert.same({}, _.drop_last(10000, list))
     end)
+
+    it("should reduce lists", function()
+        local add = spy.new(_.add)
+        assert.equals(15, _.reduce(add, 0, { 1, 2, 3, 4, 5 }))
+        assert.spy(add).was_called(5)
+        assert.spy(add).was_called_with(0, 1)
+        assert.spy(add).was_called_with(1, 2)
+        assert.spy(add).was_called_with(3, 3)
+        assert.spy(add).was_called_with(6, 4)
+        assert.spy(add).was_called_with(10, 5)
+    end)
 end)