Lambda functiona return value parametrized with auto and C++14 in-then-else codegen to support type deduction on if-then-else return type

Author: afernandez90

src/common/Functions.scala

@@ -350,8 +350,8 @@ trait CGenFunctions extends CGenEffect with BaseGenFunctions {
   override def emitNode(sym: Sym[Any], rhs: Def[Any]) = rhs match {
     case e@Lambda(fun, x, y) =>
       val retType = remap(getBlockResult(y).tp)
-      stream.println("function<"+retType+"("+
-    		  remap(x.tp)+")> "+quote(sym)+
+      val retTp = if (cppExplicitFunRet == "true") "function<"+retType+"("+remap(x.tp)+")>" else "auto"
+      stream.println(retTp+" "+quote(sym)+
     		  " = [&]("+remap(x.tp)+" "+quote(x)+") {")
       emitBlock(y)
       val z = getBlockResult(y)

src/common/IfThenElse.scala

@@ -384,14 +384,17 @@ trait CGenIfThenElse extends CGenEffect with BaseGenIfThenElse {
             emitBlock(b)
             stream.println("}")
           case _ =>
-            stream.println("%s %s;".format(remap(sym.tp),quote(sym)))
-            stream.println("if (" + quote(c) + ") {")
-            emitBlock(a)
-            stream.println("%s = %s;".format(quote(sym),quote(getBlockResult(a))))
-            stream.println("} else {")
-            emitBlock(b)
-            stream.println("%s = %s;".format(quote(sym),quote(getBlockResult(b))))
-            stream.println("}")
+            val ten = quote(sym) + "True"
+            val fen = quote(sym) + "False"
+            def emitCondFun[T: Manifest](fname: String, block: Block[T]) {
+              stream.println("auto " + fname + " = [&]() {");
+              emitBlock(block)
+              stream.println("return " + quote(getBlockResult(block)) + ";")
+              stream.println("};")
+            }
+            emitCondFun(ten, a)
+            emitCondFun(fen, b)
+            stream.println("auto " + quote(sym) + " = " + quote(c) + " ? " + ten + "() : " + fen + "();")
         }
         /*
         val booll = remap(sym.tp).equals("void")

src/internal/Config.scala

@@ -8,4 +8,7 @@ trait Config {
 
   // memory management type for C++ target (refcnt or gc)
   val cppMemMgr = System.getProperty("lms.cpp.memmgr","malloc")
+  
+  // explicit return type of lambda functions (allows recursive functions but is less generic)
+  val cppExplicitFunRet = System.getProperty("lms.cpp.explicitFunRet","true")
 }