Add string interpolation

Test.hx

@@ -96,6 +96,11 @@ class Test extends TestCase {
 		assertScript("var a:Array<Dynamic>=[1,2,4]; a[2]", 4, null, true);
 		assertScript("/**/0", 0);
 		assertScript("x=1;x*=-2", -2);
+		assertScript("'$$'", "$");
+		assertScript("'$x'", 10, { x:10 });
+		assertScript("'${x + 5}'", 15, { x:10 });
+		assertScript("'h$s'", "hscript", { s:"script" });
+		assertScript("'${function(x) {return x * x;}(3)}'", 9);
 	}
 
 	function testMap():Void {

hscript/Expr.hx

@@ -27,7 +27,7 @@ package hscript;
 enum Const {
 	CInt( v : Int );
 	CFloat( f : Float );
-	CString( s : String );
+	CString( s : String, ?interpolated:Bool );
 	#if !haxe3
 	CInt32( v : haxe.Int32 );
 	#end

hscript/Parser.hx

@@ -310,6 +310,12 @@ class Parser {
 				e = mk(EIdent(id));
 			return parseExprNext(e);
 		case TConst(c):
+			switch (c) {
+				case CString(s, interpolated):
+					if (interpolated)
+						return parseExprNext(interpolate(s));
+				default:
+			}
 			return parseExprNext(mk(EConst(c)));
 		case TPOpen:
 			var e = parseExpr();
@@ -389,6 +395,70 @@ class Parser {
 			return unexpected(tk);
 		}
 	}
+
+	function interpolate(s:String) {
+		var exprs:Array<Expr> = [];
+		var dollarIndex = s.indexOf('$');
+
+		while (dollarIndex > -1) {
+			var i = dollarIndex;
+			var char = s.charAt(++i);
+			switch (char) {
+				case '$':
+					s = s.substring(0, i) + s.substr(i + 1);
+				case '{':
+					var expr = "";
+					var depth = 0;
+
+					var precedingSub = s.substring(0, i - 1);
+					if (precedingSub != "")
+						exprs.push(mk(EConst(CString(precedingSub))));
+
+					while (i < s.length) {
+						char = s.charAt(++i);
+						if (char == '{')
+							depth++;
+						else if (char == '}') {
+							depth--;
+							if (depth < 0)
+								break;
+						}
+						expr += char;
+					}
+
+					exprs.push(parseString(expr #if hscriptPos, origin #end));
+					s = s.substr(i + 1);
+				case c if (c == '_' || c >= 'a' && c <= 'z' || c >= 'A' && c <= 'Z'): // [a-zA-Z_]
+					var ident = c;
+					var precedingSub = s.substring(0, i - 1);
+					if (precedingSub != "")
+						exprs.push(mk(EConst(CString(precedingSub))));
+					while (true) {
+						char = s.charAt(++i);
+						if (char == '_' 
+						|| char >= 'a' && char <= 'z' 
+						|| char >= 'A' && char <= 'Z' 
+						|| char >= '0' && char <= '9') // [a-zA-Z0-9_]
+							ident += char;
+						else break;
+					}
+					exprs.push(mk(EIdent(ident)));
+					s = s.substr(i);
+			}
+			dollarIndex = s.indexOf('$', i);
+		}
+
+		if (exprs.length == 0)
+			exprs.push(mk(EConst(CString(s))));
+
+		var expr = exprs[0];
+		for (i in 1...exprs.length) {
+			var nextExpr = exprs[i];
+			expr = mk(EBinop('+', expr, nextExpr));
+		}
+
+		return expr;
+	}
 
 	function mapCompr( tmp : String, e : Expr ) {
 		var edef = switch( expr(e) ) {
@@ -1070,7 +1140,7 @@ class Parser {
 			case 125: return TBrClose;
 			case 91: return TBkOpen;
 			case 93: return TBkClose;
-			case 39: return TConst( CString(readString(39)) );
+			case 39: return TConst( CString(readString(39), true) );
 			case 34: return TConst( CString(readString(34)) );
 			case 63: return TQuestion;
 			case 58: return TDoubleDot;