systems can be queries themselves

README.md

@@ -671,6 +671,29 @@ The [`evolved.process`](#evolvedprocess) function is used to process systems. It
 function evolved.process(...) end
 ```
 
+If you don't specify a query for the system, the system itself will be treated as a query. This means the system can contain `evolved.INCLUDES` and `evolved.EXCLUDES` fragments, and it will be processed according to them. This is useful for creating systems with unique queries that don't need to be reused in other systems.
+
+```lua
+local evolved = require 'evolved'
+
+local health = evolved.id()
+
+local system = evolved.builder()
+    :include(health)
+    :execute(function(chunk, entity_list, entity_count)
+        local health_components = chunk:components(health)
+
+        for i = 1, entity_count do
+            print(i)
+            health_components[i] = math.max(
+                health_components[i] - 1,
+                0)
+        end
+    end):spawn()
+
+evolved.process(system)
+```
+
 To group systems together, you can use the [`evolved.GROUP`](#evolvedgroup) fragment. Systems with a specified group will be processed when you call the [`evolved.process`](#evolvedprocess) function with this group. For example, you can group all physics systems together and process them in one [`evolved.process`](#evolvedprocess) call.
 
 ```lua
@@ -1125,6 +1148,10 @@ builder_mt:destruction_policy :: id -> builder
 
 # Changelog
 
+## vX.X.X-dev
+
+- Systems can be queries themselves
+
 ## v1.0.0
 
 - Initial release

develop/all.lua

@@ -1,6 +1,9 @@
 require 'develop.example'
-require 'develop.unbench'
 require 'develop.untests'
+
+require 'develop.testing.system_as_query_tests'
+
+require 'develop.unbench'
 require 'develop.usbench'
 
 local basics = require 'develop.basics'

develop/testing/system_as_query_tests.lua

@@ -0,0 +1,128 @@
+local evo = require 'evolved'
+
+do
+    local f1, f2, f3 = evo.id(3)
+
+    local q1e3 = evo.builder():include(f1):exclude(f3):spawn()
+    local q2e3 = evo.builder():include(f2):exclude(f3):spawn()
+
+    local e1 = evo.builder():set(f1, 1):spawn()
+    local e12 = evo.builder():set(f1, 11):set(f2, 12):spawn()
+    local e2 = evo.builder():set(f2, 2):spawn()
+    local e23 = evo.builder():set(f2, 23):set(f3, 3):spawn()
+
+    local c1 = evo.chunk(f1)
+    local c12 = evo.chunk(f1, f2)
+    local c2 = evo.chunk(f2)
+
+    do
+        local _, entity_list, entity_count = evo.chunk(f2, f3)
+        assert(entity_count == 1 and entity_list[1] == e23)
+    end
+
+    do
+        local entity_sum = 0
+
+        local s = evo.builder()
+            :query(q1e3)
+            :execute(function(chunk, entity_list, entity_count)
+                for i = 1, entity_count do
+                    entity_sum = entity_sum + entity_list[i]
+                end
+
+                if chunk == c1 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e1)
+                elseif chunk == c12 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e12)
+                else
+                    assert(false, "Unexpected chunk: " .. tostring(chunk))
+                end
+            end):spawn()
+
+        evo.process(s)
+
+        assert(entity_sum == e1 + e12)
+    end
+
+    do
+        local entity_sum = 0
+
+        local s = evo.builder()
+            :query(q2e3)
+            :execute(function(chunk, entity_list, entity_count)
+                for i = 1, entity_count do
+                    entity_sum = entity_sum + entity_list[i]
+                end
+
+                if chunk == c12 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e12)
+                elseif chunk == c2 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e2)
+                else
+                    assert(false, "Unexpected chunk: " .. tostring(chunk))
+                end
+            end):spawn()
+
+        evo.process(s)
+
+        assert(entity_sum == e12 + e2)
+    end
+
+    do
+        local entity_sum = 0
+
+        local s = evo.builder()
+            :include(f1)
+            :exclude(f3)
+            :execute(function(chunk, entity_list, entity_count)
+                for i = 1, entity_count do
+                    entity_sum = entity_sum + entity_list[i]
+                end
+
+                if chunk == c1 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e1)
+                elseif chunk == c12 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e12)
+                else
+                    assert(false, "Unexpected chunk: " .. tostring(chunk))
+                end
+            end):spawn()
+
+        evo.process(s)
+
+        assert(entity_sum == e1 + e12)
+    end
+
+    do
+        local entity_sum = 0
+
+        local s = evo.builder()
+            :include(f2)
+            :exclude(f3)
+            :execute(function(chunk, entity_list, entity_count)
+                for i = 1, entity_count do
+                    entity_sum = entity_sum + entity_list[i]
+                end
+
+                if chunk == c12 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e12)
+                elseif chunk == c2 then
+                    assert(entity_count == 1)
+                    assert(entity_list[1] == e2)
+                else
+                    assert(false, "Unexpected chunk: " .. tostring(chunk))
+                end
+            end):spawn()
+
+        evo.process(s)
+
+        assert(entity_sum == e12 + e2)
+    end
+end

evolved.lua

@@ -2727,6 +2727,7 @@ end
 
 ---@param system evolved.system
 local function __system_process(system)
+    ---@type evolved.query?, evolved.execute?, evolved.prologue?, evolved.epilogue?
     local query, execute, prologue, epilogue = __evolved_get(system,
         __QUERY, __EXECUTE, __PROLOGUE, __EPILOGUE)
 
@@ -2738,16 +2739,14 @@ local function __system_process(system)
         end
     end
 
-    if query and execute then
+    if execute then
         __evolved_defer()
-        do
-            for chunk, entity_list, entity_count in __evolved_execute(query) do
-                local success, result = __lua_pcall(execute, chunk, entity_list, entity_count)
+        for chunk, entity_list, entity_count in __evolved_execute(query or system) do
+            local success, result = __lua_pcall(execute, chunk, entity_list, entity_count)
 
-                if not success then
-                    __evolved_commit()
-                    __error_fmt('system execution failed: %s', result)
-                end
+            if not success then
+                __evolved_commit()
+                __error_fmt('system execution failed: %s', result)
             end
         end
         __evolved_commit()