Merge pull request #4 from Nymphium/multi-handler

🎉 add nulti-effect handler

Author: Nymphium

spec/async_await.lua

@@ -1,7 +1,7 @@
 -- https://github.com/ocamllabs/ocaml-effects-tutorial/blob/master/sources/solved/async_await.ml
 
 local eff = require('src/eff')
-local Eff, perform, handler = eff.Eff, eff.perform, eff.handler
+local Eff, perform, handlers = eff.Eff, eff.perform, eff.handlers
 
 local imut = require('spec/utils/imut')
 local ref = require('spec/utils/ref')
@@ -16,15 +16,19 @@ local Done = function(a)
   return { a, cls = "done" }
 end
 
-local AEff = Eff("AEff")
+local Async = Eff("Async")
 local async = function(f)
-  return perform(AEff{ f, cls = "async" })
+  return perform(Async(f))
 end
+
+local Yield = Eff("Yield")
 local yield = function()
-  return perform(AEff{ cls = "yield" })
+  return perform(Yield())
 end
+
+local Await = Eff("Await")
 local await = function(p)
-  return perform(AEff{ p, cls = "await" })
+  return perform(Await(p))
 end
 
 -- queue
@@ -36,14 +40,13 @@ end
 local dequeue = function()
   local f = table.remove(q, 1)
   if f then
-    local m = f()
-    return m
+    return f()
   end
 end
 
 local run = function(main)
   local function fork(pr, main)
-    return handler(AEff,
+    return handlers(
       function(v)
         local pp = pr:get()
         local l
@@ -61,17 +64,17 @@ local run = function(main)
         pr(Done(v))
         return dequeue()
       end,
-      function(k, c)
-        if c.cls == "async" then
-          local f = c[1]
+
+      {Async, function(k, f)
           local pr_ = ref(Waiting{})
           enqueue(function() return k(pr_) end)
           return fork(pr_, f)
-        elseif c.cls == "yield" then
+      end},
+      {Yield, function(k)
           enqueue(function() return k() end)
           return dequeue()
-        elseif c.cls == "await" then
-          local p = c[1]
+      end},
+      {Await, function(k, p)
           local pp = p:get()
 
           if pp.cls == "done" then
@@ -80,8 +83,7 @@ local run = function(main)
             p(Waiting(imut.cons(k, pp[1])))
             return dequeue()
           end
-        end
-      end)(main)
+        end})(main)
   end
 
   return fork(ref(Waiting{}), main)

spec/state2.lua

@@ -1,41 +1,44 @@
 -- https://github.com/ocamllabs/ocaml-effects-tutorial/blob/master/sources/solved/state2.ml
 
 local eff = require('src/eff')
-local Eff, perform, handler = eff.Eff, eff.perform, eff.handler
+local Eff, perform, handlers = eff.Eff, eff.perform, eff.handlers
 
 local imut = require('spec/utils/imut')
 
 local State = function()
-  local State = Eff("State")
+  local Get = Eff("Get")
+  local Put = Eff("Put")
+  local History = Eff("History")
+
   local get = function()
-    return perform(State{ cls = "Get" })
+    return perform(Get())
   end
   local put = function(v)
-    return perform(State{ v, cls = "Put" })
+    return perform(Put(v))
   end
   local history = function()
-    return perform(State{ cls = "History" })
+    return perform(History())
   end
 
   local run = function(f, init)
-    local comp = handler(State,
-    function() return function() end end,
-    function(k, c)
-      if c.cls == "Get" then
-        return function(s, h)
-          return k(s)(s, h)
-        end
-      elseif c.cls == "Put" then
-        return function(_, h)
-          local s_ = c[1]
-          return k()(s_, imut.cons(s_, h))
-        end
-      elseif c.cls == "History" then
-        return function(s, h)
-          return k(imut.rev(h))(s, imut.cp(h))
-        end
-      end
-    end)(f)
+    local comp = handlers(
+      function() return function() end end,
+        {Get, function(k)
+          return function(s, h)
+            return k(s)(s, h)
+          end
+        end},
+        {Put, function(k, v)
+          return function(_, h)
+            return k()(v, imut.cons(v, h))
+          end
+        end},
+        {History, function(k)
+          return function(s, h)
+            return k(imut.rev(h))(s, imut.cp(h))
+          end
+        end}
+    )(f)
 
     return comp(init, {})
   end

src/eff.lua

@@ -1,7 +1,13 @@
 local create = coroutine.create
 local resume = coroutine.resume
 local yield = coroutine.yield
-local unpack = table.unpack or unpack
+local unpack0 = table.unpack or unpack
+
+local unpack = function(t)
+  if t and #t > 0 then
+    return unpack0(t)
+  end
+end
 
 local Eff
 do
@@ -59,6 +65,27 @@ local is_eff_obj = function(obj)
   return type(obj) == "table" and (obj.cls == Eff.cls or obj.cls == Resend.cls)
 end
 
+local function get_effh(eff, effeffhs)
+  eff = tostring(eff)
+
+  for i = 1, #effeffhs do
+    if tostring(effeffhs[i][1]) == eff then
+      return effeffhs[i][2]
+    end
+  end
+end
+
+local function handle_error_message(r)
+  if type(r) == "string" and
+  (r:match("attempt to yield from outside a coroutine")
+   or r:match("cannot resume dead coroutine"))
+  then
+    return error("continuation cannot be performed twice")
+  else
+    return error(r)
+  end
+end
+
 local handler
 handler = function(eff, vh, effh)
   local is_the_eff = function(it)
@@ -72,7 +99,7 @@ handler = function(eff, vh, effh)
     local continue
 
     local rehandle = function(arg, k)
-      return handler(eff, function(...) return continue(gr, ...) end, effh)(function()
+      return handler(eff, function(args) return continue(gr, unpack(args)) end, effh)(function()
         return k(arg)
       end)
     end
@@ -108,14 +135,66 @@ handler = function(eff, vh, effh)
     continue = function(co, arg)
       local st, r = resume(co, arg)
       if not st then
-        if type(r) == "string" and
-        (r:match("attempt to yield from outside a coroutine")
-         or r:match("cannot resume dead coroutine"))
-        then
-            return error("continuation cannot be performed twice")
+        return handle_error_message(r)
+      else
+        return handle(r)
+      end
+    end
+
+    return continue(gr, nil)
+  end
+end
+
+local handlers
+handlers = function(vh, ...)
+  local effeffhs = {...}
+
+  return function(th)
+    local gr = create(th)
+
+    local handle
+    local continue
+
+    local rehandles = function(arg, k)
+      return handlers(function(...) return continue(gr, ...) end, unpack(effeffhs))(function()
+        return k(arg)
+      end)
+    end
+
+    handle = function(r)
+      if not is_eff_obj(r) then
+        return vh(r)
+      end
+
+      if r.cls == Eff.cls then
+        local effh = get_effh(r.eff, effeffhs)
+        if effh then
+          return effh(function(arg)
+            return continue(gr, arg)
+          end, unpack(r.arg))
+        else
+          return Resend(r, function(arg)
+            return continue(gr, arg)
+          end)
+        end
+      elseif r.cls == Resend.cls then
+        local effh = get_effh(r.eff, effeffhs)
+        if effh then
+          return effh(function(arg)
+            return rehandles(arg, r.continue)
+          end, unpack(r.arg))
         else
-          return error(r)
+          return Resend(r, function(arg)
+            return rehandles(arg, r.continue)
+          end)
         end
+      end
+    end
+
+    continue = function(co, arg)
+      local st, r = resume(co, arg)
+      if not st then
+        return handle_error_message(r)
       else
         return handle(r)
       end
@@ -125,9 +204,11 @@ handler = function(eff, vh, effh)
   end
 end
 
+
 return {
   Eff = Eff,
   perform = yield,
   handler = handler,
+  handlers = handlers
 }