Merge branch 'master' of https://github.com/saig0/feel.git

README.md

@@ -1,4 +1,104 @@
 # FEEL 
-a parser and interpreter for FEEL (friendly enough expression language) written in scala.
+A parser and interpreter for FEEL (friendly enough expression language) written in scala. 
 
+FEEL is a part of the [DMN Spec](http://www.omg.org/spec/DMN/) and is designed to write expressions and conditions in a simple way what can easily understand by business professionals and developers.
+S-FEEL is a subset of FEEL that can be used for simple expressions and conditions. Mostly, it should used for decision tables.
 
+## Goal
+Currently, the goal of the parser and interpreter is to support S-FEEL, so that it can used for decision tables.
+
+## Supported Language Features
+* data types: number, string, boolean, date
+* simple unary tests: compare operators ('<', '<=', '>', '>=', equal), interval, negation, combination of multiple tests
+* qualified names
+
+## Current Limitations
+* unsupported data types: time, duration
+* no simple expressions
+* the input of the simple unary test should be given as context entry 'cellInput'
+
+# How to use 
+The parser and interpreter can be integrated as dependency or as jar which include all dependencies (size of ~ 7mb).
+Make sure you have build and deploy it (locally) before. It is not deployed in a public repository yet.
+
+## Native Way
+There is a class 'FeelEngine' that can be used to parse and evaluate a given expression. This class can be called from a scala or java program. 
+
+```scala
+object AnyProgram {
+
+  val engine = new FeelEngine
+
+  def feel(expression: String, context: Map[String, Any]) {
+
+    val result: EvalResult = engine.evalSimpleUnaryTest(expression, context)
+
+    result match {
+      case EvalValue(value)   =>  // ...
+      case EvalFailure(error) =>  // ...
+      case ParseFailure(error) => // ...
+    }
+  }
+
+}
+```
+
+## As Script Engine
+The spec [JSR 223](https://www.jcp.org/en/jsr/detail?id=223) is implemented so that it can be used as script engine. It is registered by name 'feel'.
+
+```scala
+object AnyProgram {
+
+  val scriptEngineManager = new ScriptEngineManager
+
+  def feel(script: String, context: ScriptContext) {
+
+    val scriptEngine: FeelScriptEngine = scriptEngineManager.getEngineByName("feel")
+
+    val result: Object = scriptEngine.eval(script, context)
+    // ...
+  }
+
+}
+```
+
+# How to build
+
+> Requirements
+* [SBT](http://www.scala-sbt.org) to build and test the application
+
+Run the tests with
+```
+sbt test
+```
+
+Build the jar including all dependencies with
+```
+sbt assemply
+```
+
+Deploy it locally with
+```
+sbt pulishLocal
+```
+
+# Examples
+Just to have a feeling how an expression can look like:
+
+## Simple Unary Test
+```
+< 42
+
+(2..4)
+
+2,4
+
+not(2,4)
+
+>= a
+
+[date("2015-09-17")..date("2015-09-19")]
+
+"good"
+
+```