README.md in fluent-plugin-simplearithmetic-0.0.1.pre vs README.md in fluent-plugin-simplearithmetic-0.0.1

@@ -22,19 +22,19 @@
   'time_start': '2001-02-03T04:05:06Z',
   'time_finish': '2001-02-03T04:06:12Z',
 }
 ```
 
-Now you can calculate with this `td-agent.conf`:
+Now you can calculate with this configuration:
 
 ```
 <match arithmetic.test>
   type simple_arithmetic
   tag calculated.test
 
   <formulas>
-    total_price   apple * 200 - orange * 100
+    total_price   apple * 200 + orange * 100
 
     # Calculation order is from up to down.
     budget   2000 - total_price
 
     # You can also use Time.iso8601
@@ -53,34 +53,92 @@
 {
 	"apple": 7,
 	"orange": 3,
 	"time_start": "2001-02-03T04:05:06Z",
 	"time_finish": "2001-02-03T04:06:12Z",
-	"total_price": 1100,
-	"budget": 900,
+	"total_price": 1700,
+	"budget": 300,
 	"time_elapsed": 66.0
 }
 ```
 
+If some fields are already defined before calculation, these fields will be overwritten.
 
+
 ## Configuration
 
+### tag
+The tag prefix for emitted event messages. Default is `simple_arithmetic`.
 
 ### undefined_variables
-1. `nil`
 
-2. `undefined` (default)
+A message such like `{'a':  20, 'x':  50}` with the formulas:
 
+```
+<formulas>
+  c   a + b
+</formulas>
+```
+
+When undefined_variables is `undefined` (default) you get `{'a':  20, 'x':  50}`. Field `'c'` will not be defined.
+
+When `nil` you get `{'a':  20, 'c': nil, 'x':  50}`.
+
+
 ### how_to_process_error
-1. `nil`
 
-2. `undefined`
+A message such like `{'a':  20, 'b':  "string"}` with the formulas:
 
-3. `error_string` (default)
+```
+<formulas>
+  c   a + b
+</formulas>
+```
 
+In ruby, this calculation will be raise an error:
 
-### tag
-The tag prefix for emitted event messages. Default is `simple_arithmetic`.
+```
+irb(main):052:0* a = 20
+=> 20
+irb(main):053:0> b = "String"
+=> "String"
+irb(main):054:0> c = a + b
+TypeError: String can't be coerced into Fixnum
+	from (irb):54:in `+'
+	from (irb):54
+	from /opt/td-agent/embedded/bin/irb:11:in `<main>'
+```
+
+When how_to_process_error is `nil` you get `{'a':  20, 'b': "string", 'c': nil}`.
+
+When `undefined`, you get `{'a':  20, 'b': "string"}`. If an error is raised in the calculation, the field will not be defined.
+
+When `error_string` (default), you get: `{'a':  20, 'b': "String", 'c'=>"String can't be coerced into Fixnum"}`. An error message will be assigned to the field.
+
+### replace_hyphen, replace_dollar
+
+All formulas will be evaluated as ruby sentences. Some json fields will not be fitted as ruby variables. For example, 
+
+```
+<formulas>
+   var-1   a + b
+   var$2   c * d
+</formulas>
+```
+
+will raise an syntax error in the initialize process of fluentd.
+
+To get rid of this case, you can set `replace_hyphen` and `replace_dollar` in the configuration and formulas.
+
+```
+replace_hyphen   __H__
+replace_dollar   __D__
+
+<formulas>
+   var__H__1   a + b
+   var__D__2   c * d
+</formulas>
+```
 
 
 ## Copyright
 
 Copyright:: Copyright (c) 2014- Takahiro Kamatani