change how values are passed to compiled template, require a buffer pos if passing buffer

README.md

@@ -138,8 +138,8 @@ first_fn = parser:load(parser:compile_to_lua("Hello "))
 second_fn = parser:load(parser:compile_to_lua("World"))
 
 buffer = {}
-parser:run(first_fn, nil, buffer)
-parser:run(second_fn, nil, buffer)
+parser:run(first_fn, nil, buffer, #buffer)
+parser:run(second_fn, nil, buffer, #buffer)
 
 print(table.concat(buffer)) -- print 'Hello World'
 ```

etlua.moon

@@ -54,7 +54,7 @@ class Compiler
     @push ...  if ...
 
   header: =>
-    @push "local _b, _b_i, _tostring, _concat, _escape = ...\n"
+    @push "local _tostring, _escape, _b, _b_i = ...\n"
 
   footer: =>
     @push "return _b"
@@ -220,14 +220,18 @@ class Parser
     fn
 
   -- takes a function from @load and executes it with correct parameters
-  run: (fn, env={}, buffer={}) =>
+  run: (fn, env={}, buffer, i, ...) =>
     combined_env = setmetatable {}, __index: (name) =>
       val = env[name]
       val = _G[name] if val == nil
       val
 
+    unless buffer
+      buffer = {}
+      i = 0
+
     setfenv fn, combined_env
-    fn buffer, #buffer, tostring, concat, html_escape
+    fn tostring, html_escape, buffer, i, ...
 
   compile_to_lua: (str, ...) =>
     success, err = @parse str

spec/etlua_spec.moon

@@ -109,7 +109,7 @@ This is my message to <%= [=[oh yeah  %>"]=] %>]]
     it "should use existing buffer", ->
       fn = compile "hello<%= 'yeah' %>"
       buff = {"first"}
-      out = fn {}, buff
+      out = fn {}, buff, #buff
       assert.same "firsthelloyeah", out
 
     it "should compile readme example", ->
@@ -119,8 +119,8 @@ This is my message to <%= [=[oh yeah  %>"]=] %>]]
       second_fn = parser\load parser\compile_to_lua "World"
 
       buffer = {}
-      parser\run first_fn, nil, buffer
-      parser\run second_fn, nil, buffer
+      parser\run first_fn, nil, buffer, #buffer
+      parser\run second_fn, nil, buffer, #buffer
 
       assert.same "Hello World", table.concat buffer