adding translation for if-then-else, some code hoisting for clarity (#…

…315)

* adding translation for if-then-else, some code hoisting for clarity

* adding test case and config for it, so it'll run in travis

* ide scraps

* polish on PR per discussion with @mcoblenz on #315

resources/tests/GanacheTests/IfThenElse.json

@@ -0,0 +1,6 @@
+{
+    "gas" : 30000000,
+    "gasprice" : "0x9184e72a000",
+    "startingeth" : 5000000,
+    "numaccts" : 1
+}

resources/tests/GanacheTests/IfThenElse.obs

@@ -0,0 +1,11 @@
+main contract IfThenElse {
+        int x;
+        transaction ifthenelse() {
+            if (true) {
+	       x = 1;
+	    } else {
+	       x = 0;
+	    }
+            return;
+        }
+}

src/main/scala/edu/cmu/cs/obsidian/codegen/CodeGenYul.scala

@@ -6,6 +6,7 @@ import edu.cmu.cs.obsidian.CompilerOptions
 import edu.cmu.cs.obsidian.parser._
 import edu.cmu.cs.obsidian.Main.{findMainContract, findMainContractName}
 import edu.cmu.cs.obsidian.typecheck.ContractType
+import edu.cmu.cs.obsidian.codegen.Switch
 
 import scala.collection.immutable.Map
 
@@ -18,6 +19,10 @@ object CodeGenYul extends CodeGenerator {
     var stateEnumMapping: Map[String, Int] = Map() // map from state name to an enum value
     var stateEnumCounter = 0  // counter indicating the next value to assign since we don't knon the total num of states
 
+    // some constants hoisted from below to avoid repeated code
+    val true_lit : Literal = Literal(LiteralKind.boolean, "true", "bool")
+    val false_lit : Literal = Literal(LiteralKind.boolean, "false", "bool")
+
     def gen(filename: String, srcDir: Path, outputPath: Path, protoDir: Path,
             options: CompilerOptions, checkedTable: SymbolTable, transformedTable: SymbolTable): Boolean = {
         // extract ast and find main contract
@@ -250,11 +255,24 @@ object CodeGenYul extends CodeGenerator {
                         assert(false, "TODO")
                         Seq()
                 }
-
-            case _ =>
-                assert(false, "TODO")
+            case IfThenElse(scrutinee,pos,neg) =>
+                val scrutinee_yul : Seq[YulStatement] = translateExpr(scrutinee)
+                if (scrutinee_yul.length > 1){
+                    assert(false,"boolean expression in conditional translates to a sequence of expressons")
+                    Seq()
+                }
+                scrutinee_yul.apply(0) match {
+                    case ExpressionStatement(sye) =>
+                        val pos_yul = pos.flatMap(translateStatement)
+                        val neg_yul = neg.flatMap(translateStatement)
+                        Seq(Switch(sye,Seq(Case(true_lit , Block(pos_yul)), Case(false_lit, Block(neg_yul)))))
+                    case e =>
+                        assert(false, "if statement built on non-expression: " + e.toString())
+                        Seq()
+                }
+            case x =>
+                assert(false, "TODO: translateStatement for " + x.toString() + " is unimplemented")
                 Seq()
-
         }
     }
 
@@ -268,9 +286,9 @@ object CodeGenYul extends CodeGenerator {
                 // we compile to int, which is s256 in yul
                 Seq(ExpressionStatement(Literal(LiteralKind.number,n.toString(),"int")))
             case TrueLiteral() =>
-                Seq(ExpressionStatement(Literal(LiteralKind.boolean, "true", "bool")))
+                Seq(ExpressionStatement(true_lit))
             case FalseLiteral() =>
-                Seq(ExpressionStatement(Literal(LiteralKind.boolean, "false", "bool")))
+                Seq(ExpressionStatement(false_lit))
             case _ =>
                 assert(false, "TODO: translation of " + e.toString() + " is not implemented")
                 Seq() // TODO unimplemented