add compile_to_lua helper function

etlua.lua

@@ -264,6 +264,13 @@ do
       setfenv(fn, combined_env)
       return fn(buffer, #buffer, tostring, concat, html_escape)
     end,
+    compile_to_lua = function(self, str)
+      local success, err = self:parse(str)
+      if not (success) then
+        return nil, err
+      end
+      return self:chunks_to_lua()
+    end,
     chunks_to_lua = function(self)
       local buffer = {
         "local _b, _b_i, _tostring, _concat, _escape = ..."

etlua.moon

@@ -199,6 +199,11 @@ class Parser
     setfenv fn, combined_env
     fn buffer, #buffer, tostring, concat, html_escape
 
+  compile_to_lua: (str) =>
+    success, err = @parse str
+    return nil, err unless success
+    @chunks_to_lua!
+
   -- generates the code of the template
   chunks_to_lua: =>
     -- todo: find a no-conflict name for locals

spec/etlua_spec.moon

@@ -112,6 +112,18 @@ This is my message to <%= [=[oh yeah  %>"]=] %>]]
       out = fn {}, buff
       assert.same "firsthelloyeah", out
 
+    it "should compile readme example", ->
+      parser = Parser!
+
+      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
+
+      assert.same "Hello World", table.concat buffer
+
   describe "Parser.in_string", ->
     cases = {
       { "hello world", false }