Merge pull request #1396 from janyou/swift-target-readme

update swift-target.md

doc/swift-target.md

@@ -1 +1,113 @@
 # ANTLR4 Language Target, Runtime for Swift
+
+### Usage
+
+#### 1. Install ANTLR4
+
+[The getting started guide](getting-started.md) should get you started.
+
+#### 2. create a Swift lexer or parser
+This is pretty much the same as creating a Java lexer or parser, except you need to specify the language target, for example:
+
+```
+$ antlr4 -Dlanguage=Swift MyGrammar.g4
+```
+For a full list of antlr4 tool options, please visit the [tool documentation page](tool-options.md).
+
+#### 3. Get the Swift ANTLR runtime
+You will find Swift runtime (framework project) in
+
+```
+antlr4/runtime/Swift 
+```
+
+#### 4. Example
+
+The example from [here](https://github.com/janyou/Antlr-Swift-Runtime/tree/master/Test)
+
+(1). Hello.g4
+
+
+```
+grammar Hello;
+r  : 'hello' ID ;          
+ID : [a-z]+ ;              
+WS : [ \t\r\n]+ -> skip ;  
+```
+
+(2). generate lexer/parser/visitor from Hello.g4 file
+
+```
+$ antlr4 -Dlanguage=Swift -visitor -o gen Hello.g4
+```
+
+in gen folder：
+
+```
+Hello.tokens
+HelloBaseListener.swift
+HelloBaseVisitor.swift
+HelloLexer.swift
+HelloLexer.tokens
+HelloLexerATN.swift
+HelloListener.swift
+HelloParser.swift
+HelloParserATN.swift
+HelloVisitor.swift 
+```
+
+(3). make a custom listener
+
+```
+public class HelloWalker: HelloBaseListener{
+    public override func enterR(_ ctx: HelloParser.RContext) {
+        print( "enterR: " + ((ctx.ID()?.getText()) ?? ""))
+    }
+
+    public override func exitR(_ ctx: HelloParser.RContext) {
+        print( "exitR  ")
+    }
+}
+
+```
+
+(4). call and run
+
+
+
+add TestHello.txt
+
+```
+hello world
+```
+
+run:
+
+```
+import Antlr4
+
+....
+
+do {
+
+	let textFileName = "TestHello.txt"
+	if let textFilePath = Bundle.main.path(forResource: textFileName, ofType: nil) {
+    	let lexer =  HelloLexer(ANTLRFileStream(textFilePath))
+    	let tokens =  CommonTokenStream(lexer)
+    	let parser = try HelloParser(tokens)
+    	let tree = try parser.r()
+    	let walker = ParseTreeWalker()
+    	try walker.walk(HelloWalker(),tree)
+	} else {
+    	print("error occur: can not open \(textFileName)")
+	}
+
+}catch ANTLRException.cannotInvokeStartRule {
+    print("error occur: CannotInvokeStartRule")
+}catch ANTLRException.recognition(let e )   {
+    print("error occur\(e)")
+}catch {
+    print("error occur")
+}
+```
+