diff --git a/bin/asc.js b/bin/asc.js
index df27a44b..6f2378bc 100644
--- a/bin/asc.js
+++ b/bin/asc.js
@@ -7,7 +7,7 @@ var assemblyscript;
 var isDev = true;
 try {
   assemblyscript = require("../dist/assemblyscript.js");
-  require("source-map-support").install();
+  try { require("source-map-support").install(); } catch (e) {} // optional
   isDev = false;
 } catch (e) {
   require("ts-node").register({ project: require("path").join(__dirname, "..", "src") });
diff --git a/package.json b/package.json
index 9de25cd5..5476d439 100644
--- a/package.json
+++ b/package.json
@@ -13,8 +13,7 @@
   "dependencies": {
     "binaryen": "40.0.0-nightly.20171209",
     "glob": "^7.1.2",
-    "minimist": "^1.2.0",
-    "source-map-support": "^0.5.0"
+    "minimist": "^1.2.0"
   },
   "devDependencies": {
     "@types/chalk": "^2.2.0",
@@ -26,6 +25,7 @@
     "chalk": "^2.3.0",
     "diff": "^3.4.0",
     "long": "^3.2.0",
+    "source-map-support": "^0.5.0",
     "ts-loader": "^3.2.0",
     "ts-node": "^4.0.2",
     "tslint": "^5.8.0",
@@ -42,15 +42,15 @@
   },
   "scripts": {
     "build": "webpack",
-    "clean": "rm dist/assemblyscript.*",
+    "clean": "node scripts/clean",
+    "lint": "tslint --project src",
     "test:config": "npm run test:config:assembly --scripts-prepend-node-path && npm run test:config:portable --scripts-prepend-node-path && npm run test:config:src --scripts-prepend-node-path",
     "test:config:assembly": "tsc --noEmit -p std/assembly --diagnostics --listFiles",
     "test:config:portable": "tsc --noEmit -p std/portable --diagnostics --listFiles",
     "test:config:src": "tsc --noEmit -p src --diagnostics --listFiles",
     "test:parser": "node tests/parser",
     "test:compiler": "node tests/compiler",
-    "test": "npm run test:config --scripts-prepend-node-path && npm run test:parser --scripts-prepend-node-path && npm run test:compiler --scripts-prepend-node-path",
-    "lint": "tslint --project src"
+    "test": "npm run test:config --scripts-prepend-node-path && npm run test:parser --scripts-prepend-node-path && npm run test:compiler --scripts-prepend-node-path"
   },
   "files": [
     "bin/",
diff --git a/scripts/clean.js b/scripts/clean.js
new file mode 100644
index 00000000..956dea95
--- /dev/null
+++ b/scripts/clean.js
@@ -0,0 +1,16 @@
+var fs = require("fs");
+var glob = require("glob");
+
+glob("*", { cwd: __dirname + "/../dist" }, (err, matches) => {
+  if (err)
+    console.log("Failed to list files in 'dist/': " + err.message);
+  else
+    matches.forEach(match => {
+      fs.unlink(__dirname + "/../dist/" + match, err => {
+        if (err)
+          console.log("Failed to delete 'dist/" + match + "': " + err.message);
+        else
+          console.log("Deleted 'dist/" + match + "'");
+      });
+    });
+});
diff --git a/src/ast.ts b/src/ast.ts
index 65ddded5..0c369463 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -2185,15 +2185,14 @@ function builderEndsWith(sb: string[], code: CharCode): bool {
 export function escapeString(str: string): string {
   var k = str.length;
   var ret = new Array<string>(k);
-  ret.length = 0;
   for (var i = 0, c: string; i < k; ++i) {
     switch (c = str.charAt(i)) {
-      case "\\": ret.push("\\\\"); break;
-      case "\"": ret.push("\\\""); break;
-      case "\r": ret.push("\\r"); break;
-      case "\n": ret.push("\\n"); break;
-      case "\0": ret.push("\\0"); break;
-      default: ret.push(c);
+      case "\\": ret[i] = "\\\\"; break;
+      case "\"": ret[i] = "\\\""; break;
+      case "\r": ret[i] = "\\r"; break;
+      case "\n": ret[i] = "\\n"; break;
+      case "\0": ret[i] = "\\0"; break;
+      default: ret[i] = c;
     }
   }
   return "\"" + ret.join("") + "\"";
diff --git a/src/builtins.ts b/src/builtins.ts
index c118e589..8985aac5 100644
--- a/src/builtins.ts
+++ b/src/builtins.ts
@@ -689,11 +689,11 @@ export function compileCall(compiler: Compiler, prototype: FunctionPrototype, ty
 
     // other
 
-    case "changetype": // changetype<T1,T2>(value: T1) -> T2
-      if (!validateCall(compiler, typeArguments, 2, operands, 1, reportNode))
+    case "changetype": // changetype<T>(value: *) -> T
+      if (!validateCall(compiler, typeArguments, 1, operands, 1, reportNode))
         return module.createUnreachable();
-      if ((typeArguments[0] == usizeType && typeArguments[1].classType) || (typeArguments[0].classType && typeArguments[1] == usizeType)) {
-        arg0 = compiler.compileExpression(operands[0], typeArguments[0]);
+      arg0 = compiler.compileExpression(operands[0], Type.void, ConversionKind.NONE);
+      if ((compiler.currentType == usizeType && typeArguments[1].classType) || (compiler.currentType.classType && typeArguments[1] == usizeType)) {
         compiler.currentType = typeArguments[1];
         return arg0;
       }
diff --git a/src/compiler.ts b/src/compiler.ts
index f54b85dd..df6e287b 100644
--- a/src/compiler.ts
+++ b/src/compiler.ts
@@ -386,7 +386,7 @@ export class Compiler extends DiagnosticEmitter {
           if (!global.isMutable) {
             initExpr = this.precomputeExpressionRef(initExpr);
             if (_BinaryenExpressionGetId(initExpr) != ExpressionId.Const) {
-              this.warning(DiagnosticCode.Compiling_constant_global_with_non_constant_initializer_as_mutable, declaration.range);
+              this.warning(DiagnosticCode.Compiling_constant_with_non_constant_initializer_as_mutable, declaration.range);
               initializeInStart = true;
             }
           } else
@@ -461,7 +461,7 @@ export class Compiler extends DiagnosticEmitter {
               initExpr = this.precomputeExpressionRef(initExpr);
               if (_BinaryenExpressionGetId(initExpr) != ExpressionId.Const) {
                 if (element.isConstant)
-                  this.warning(DiagnosticCode.Compiling_constant_global_with_non_constant_initializer_as_mutable, declaration.range);
+                  this.warning(DiagnosticCode.Compiling_constant_with_non_constant_initializer_as_mutable, declaration.range);
                 initInStart = true;
               }
             }
@@ -476,7 +476,7 @@ export class Compiler extends DiagnosticEmitter {
               this.module.createI32(1)
             );
             if (element.isConstant)
-              this.warning(DiagnosticCode.Compiling_constant_global_with_non_constant_initializer_as_mutable, declaration.range);
+              this.warning(DiagnosticCode.Compiling_constant_with_non_constant_initializer_as_mutable, declaration.range);
             initInStart = true;
           }
           if (initInStart) {
@@ -1029,7 +1029,8 @@ export class Compiler extends DiagnosticEmitter {
               }
               this.currentFunction.locals.set(name, local);
               continue;
-            }
+            } else
+              this.warning(DiagnosticCode.Compiling_constant_with_non_constant_initializer_as_mutable, declaration.range);
           } else {
             this.error(DiagnosticCode._const_declarations_must_be_initialized, declaration.range);
           }
diff --git a/src/diagnosticMessages.generated.ts b/src/diagnosticMessages.generated.ts
index fa8388bb..3d1e7118 100644
--- a/src/diagnosticMessages.generated.ts
+++ b/src/diagnosticMessages.generated.ts
@@ -6,7 +6,7 @@ export enum DiagnosticCode {
   Operation_not_supported = 102,
   Operation_is_unsafe = 103,
   Cannot_export_a_mutable_global = 104,
-  Compiling_constant_global_with_non_constant_initializer_as_mutable = 105,
+  Compiling_constant_with_non_constant_initializer_as_mutable = 105,
   Type_0_cannot_be_changed_to_type_1 = 106,
   Unterminated_string_literal = 1002,
   Identifier_expected = 1003,
@@ -87,7 +87,7 @@ export function diagnosticCodeToString(code: DiagnosticCode): string {
     case 102: return "Operation not supported.";
     case 103: return "Operation is unsafe.";
     case 104: return "Cannot export a mutable global.";
-    case 105: return "Compiling constant global with non-constant initializer as mutable.";
+    case 105: return "Compiling constant with non-constant initializer as mutable.";
     case 106: return "Type '{0}' cannot be changed to type '{1}'.";
     case 1002: return "Unterminated string literal.";
     case 1003: return "Identifier expected.";
diff --git a/src/diagnosticMessages.json b/src/diagnosticMessages.json
index 612ce7bd..2a4444f8 100644
--- a/src/diagnosticMessages.json
+++ b/src/diagnosticMessages.json
@@ -4,7 +4,7 @@
   "Operation not supported.": 102,
   "Operation is unsafe.": 103,
   "Cannot export a mutable global.": 104,
-  "Compiling constant global with non-constant initializer as mutable.": 105,
+  "Compiling constant with non-constant initializer as mutable.": 105,
   "Type '{0}' cannot be changed to type '{1}'.": 106,
 
   "Unterminated string literal.": 1002,
diff --git a/src/module.ts b/src/module.ts
index 445f8058..45381f28 100644
--- a/src/module.ts
+++ b/src/module.ts
@@ -264,7 +264,7 @@ export class Module {
   static create(): Module {
     var module = new Module();
     module.ref = _BinaryenModuleCreate();
-    module.lit = changetype<usize,BinaryenLiteral>(Heap.allocate(16));
+    module.lit = changetype<BinaryenLiteral>(Heap.allocate(16));
     module.noEmit = false;
     return module;
   }
@@ -274,18 +274,18 @@ export class Module {
     try {
       var module = new Module();
       module.ref = _BinaryenModuleRead(cArr, buffer.length);
-      module.lit = changetype<usize,BinaryenLiteral>(Heap.allocate(16));
+      module.lit = changetype<BinaryenLiteral>(Heap.allocate(16));
       module.noEmit = false;
       return module;
     } finally {
-      Heap.dispose(changetype<usize,usize>(cArr));
+      Heap.dispose(changetype<usize>(cArr));
     }
   }
 
   static createStub(): Module {
     var module = new Module();
     module.ref = 0;
-    module.lit = changetype<usize,BinaryenLiteral>(0);
+    module.lit = changetype<BinaryenLiteral>(0);
     module.noEmit = true;
     return module;
   }
@@ -806,7 +806,7 @@ export class Module {
   dispose(): void {
     if (!this.ref) return; // sic
     _BinaryenModuleDispose(this.ref);
-    Heap.dispose(changetype<BinaryenLiteral, usize>(this.lit));
+    Heap.dispose(changetype<usize>(this.lit));
   }
 
   createRelooper(): Relooper {
diff --git a/std/assembly.d.ts b/std/assembly.d.ts
index 01f618b0..a475268c 100644
--- a/std/assembly.d.ts
+++ b/std/assembly.d.ts
@@ -162,7 +162,7 @@ declare const HEAP_BASE: usize;
 /** Determines the byte size of the specified core or class type. Compiles to a constant. */
 declare function sizeof<T>(): usize;
 /** Changes the type of a value to another one. Useful for casting class instances to their pointer values and vice-versa. */
-declare function changetype<T1,T2>(value: T1): T2;
+declare function changetype<T>(value: any): T;
 /** Tests if a 32-bit or 64-bit float is `NaN`. */
 declare function isNaN<T = f32 | f64>(value: T): bool;
 /** Tests if a 32-bit or 64-bit float is finite, that is not `NaN` or +/-`Infinity`. */
diff --git a/std/assembly/array.ts b/std/assembly/array.ts
index 394ec3a0..498fa8fb 100644
--- a/std/assembly/array.ts
+++ b/std/assembly/array.ts
@@ -18,10 +18,10 @@ export class Array<T> {
   }
 
   dispose(): void {
-    store<i64>(changetype<this,usize>(this), 0);
+    store<i64>(changetype<usize>(this), 0);
     Heap.dispose(this.ptr);
     this.ptr = 0;
-    Heap.dispose(changetype<this,usize>(this));
+    Heap.dispose(changetype<usize>(this));
   }
 
   // TODO
diff --git a/std/assembly/heap.ts b/std/assembly/heap.ts
index e0181545..a33e4bd9 100644
--- a/std/assembly/heap.ts
+++ b/std/assembly/heap.ts
@@ -2,7 +2,7 @@ const ALIGN_LOG2: usize = 3;
 const ALIGN_SIZE: usize = 1 << ALIGN_LOG2;
 const ALIGN_MASK: usize = ALIGN_SIZE - 1;
 
-let HEAP_OFFSET: usize = HEAP_BASE; // HEAP_BASE is a constant generated by the compiler
+var HEAP_OFFSET: usize = HEAP_BASE; // HEAP_BASE is a constant generated by the compiler
 
 // TODO: maybe tlsf
 
@@ -15,11 +15,11 @@ export class Heap {
 
   static allocate(size: usize): usize {
     if (!size) return 0;
-    const len: i32 = current_memory();
+    var len: i32 = current_memory();
     if (HEAP_OFFSET + size > <usize>len << 16)
       if(grow_memory(max<i32>(<i32>ceil<f64>(<f64>size / 65536), len * 2 - len)) < 0)
         unreachable();
-    const ptr: usize = HEAP_OFFSET;
+    var ptr: usize = HEAP_OFFSET;
     if ((HEAP_OFFSET += size) & ALIGN_MASK) // align next offset
       HEAP_OFFSET = (HEAP_OFFSET | ALIGN_MASK) + 1;
     return ptr;
@@ -33,8 +33,8 @@ export class Heap {
     assert(dest >= HEAP_BASE);
 
     // the following is based on musl's implementation of memcpy
-    let dst: usize = dest;
-    let w: u32, x: u32;
+    var dst: usize = dest;
+    var w: u32, x: u32;
 
     // copy 1 byte each until src is aligned to 4 bytes
     while (n && src % 4) {
@@ -180,7 +180,7 @@ export class Heap {
     // the following is based on musl's implementation of memset
     if (!n) return dest;
 
-    let s: usize = dest;
+    var s: usize = dest;
 
     // Fill head and tail with minimal branching
     store<u8>(s, c); store<u8>(s + n - 1, c);
@@ -192,12 +192,12 @@ export class Heap {
     if (n <= 8) return dest;
 
     // Align to 4 bytes
-    let k: usize = -s & 3;
+    var k: usize = -s & 3;
     s += k;
     n -= k;
     n &= -4;
 
-    let c32: u32 = -1 / 255 * c;
+    var c32: u32 = -1 / 255 * c;
 
     // Fill head and tail in preparation of setting 32 bytes at a time
     store<u32>(s, c32);
@@ -223,7 +223,7 @@ export class Heap {
     n -= k;
 
     // Set 32 bytes at a time
-    let c64: u64 = <u64>c32 | (<u64>c32 << 32);
+    var c64: u64 = <u64>c32 | (<u64>c32 << 32);
     while (n >= 32) {
       store<u64>(s, c64);
       store<u64>(s + 8, c64);
diff --git a/std/assembly/string.ts b/std/assembly/string.ts
index 734220c8..ec546071 100644
--- a/std/assembly/string.ts
+++ b/std/assembly/string.ts
@@ -1,4 +1,4 @@
-const EMPTY: String = changetype<string,String>("");
+const EMPTY: String = changetype<String>("");
 
 @global()
 export class String {
@@ -29,10 +29,10 @@ export class String {
     assert(this != null);
     if (pos < 0 || pos >= this.length)
       return -1; // undefined
-    let first: i32 = <i32>load<u16>(this.ptr + (<usize>pos << 1));
+    var first = <i32>load<u16>(this.ptr + (<usize>pos << 1));
     if (first < 0xD800 || first > 0xDBFF || pos + 1 == this.length)
       return first;
-    let second: i32 = <i32>load<u16>(this.ptr + ((<usize>pos + 1) << 1));
+    var second = <i32>load<u16>(this.ptr + ((<usize>pos + 1) << 1));
     if (second < 0xDC00 || second > 0xDFFF)
       return first;
     return ((first - 0xD800) << 10) + (second - 0xDC00) + 0x10000;
@@ -42,9 +42,9 @@ export class String {
   concat(other: String): String {
     assert(this != null);
     assert(other != null);
-    const thisLen: isize = this.length;
-    const otherLen: isize = other.length;
-    const len: usize = thisLen + otherLen;
+    var thisLen: isize = this.length;
+    var otherLen: isize = other.length;
+    var len: usize = thisLen + otherLen;
     return new String(
       Heap.copy(
         Heap.copy(
@@ -62,9 +62,9 @@ export class String {
   endsWith(searchString: String, endPosition: i32 = 0x7fffffff): bool {
     assert(this != null);
     assert(searchString != null);
-    let end: isize = <isize>min<i32>(max<i32>(endPosition, 0), this.length);
-    let searchLength: isize = searchString.length;
-    let start: isize = end - searchLength;
+    var end: isize = <isize>min<i32>(max<i32>(endPosition, 0), this.length);
+    var searchLength: isize = searchString.length;
+    var start: isize = end - searchLength;
     if (start < 0)
       return false;
     return !Heap.compare(this.ptr + (start << 1), searchString.ptr, searchLength << 1);
@@ -85,11 +85,11 @@ export class String {
   indexOf(searchString: String, position: i32 = 0): i32 {
     assert(this != null);
     assert(searchString != null);
-    let pos: isize = position;
-    let len: isize = this.length;
-    let start: isize = min<isize>(max<isize>(pos, 0), len);
-    let searchLen: isize = searchString.length;
-    for (let k: usize = start; <isize>k + searchLen <= len; ++k)
+    var pos: isize = position;
+    var len: isize = this.length;
+    var start: isize = min<isize>(max<isize>(pos, 0), len);
+    var searchLen: isize = searchString.length;
+    for (var k: usize = start; <isize>k + searchLen <= len; ++k)
       if (!Heap.compare(this.ptr + (k << 1), searchString.ptr, searchLen << 1))
         return <i32>k;
     return -1;
@@ -98,10 +98,10 @@ export class String {
   startsWith(searchString: String, position: i32 = 0): bool {
     assert(this != null);
     assert(searchString != null);
-    let pos: isize = position;
-    let len: isize = this.length;
-    let start: isize = min<isize>(max<isize>(position, 0), len);
-    let searchLength: isize = searchString.length;
+    var pos: isize = position;
+    var len: isize = this.length;
+    var start: isize = min<isize>(max<isize>(position, 0), len);
+    var searchLength: isize = searchString.length;
     if (searchLength + start > len)
       return false;
     return !Heap.compare(this.ptr + (start << 1), searchString.ptr, searchLength << 1);
@@ -109,12 +109,12 @@ export class String {
 
   substr(start: i32, length: i32 = i32.MAX_VALUE): String {
     assert(this != null);
-    let intStart: isize = start;
-    let end: isize = length;
-    let size: isize = this.length;
+    var intStart: isize = start;
+    var end: isize = length;
+    var size: isize = this.length;
     if (intStart < 0)
       intStart = max<isize>(size + intStart, 0);
-    let resultLength: isize = min<isize>(max<isize>(end, 0), size - intStart);
+    var resultLength: isize = min<isize>(max<isize>(end, 0), size - intStart);
     if (resultLength < 0)
       return EMPTY;
     return new String(this.ptr + (intStart << 1), <i32>resultLength);
@@ -122,11 +122,11 @@ export class String {
 
   substring(start: i32, end: i32 = i32.MAX_VALUE): String {
     assert(this != null);
-    let len: i32 = this.length;
-    let finalStart: i32 = min<i32>(max<i32>(start, 0), len);
-    let finalEnd: i32 = min<i32>(max<i32>(end, 0), len);
-    let from: i32 = min<i32>(finalStart, finalEnd);
-    let to: i32 = max<i32>(finalStart, finalEnd);
+    var len = this.length;
+    var finalStart = min<i32>(max<i32>(start, 0), len);
+    var finalEnd = min<i32>(max<i32>(end, 0), len);
+    var from = min<i32>(finalStart, finalEnd);
+    var to = max<i32>(finalStart, finalEnd);
     len = to - from;
     if (!len)
       return EMPTY;
@@ -137,10 +137,10 @@ export class String {
 
   trim(): String {
     assert(this != null);
-    let length: usize = this.length;
+    var length: usize = this.length;
     while (length && isWhiteSpaceOrLineTerminator(load<u16>(this.ptr + (length << 1))))
       --length;
-    let start: usize = 0;
+    var start: usize = 0;
     while (start < length && isWhiteSpaceOrLineTerminator(load<u16>(this.ptr + (start << 1)))) {
       ++start; --length;
     }
@@ -153,8 +153,8 @@ export class String {
 
   trimLeft(): String {
     assert(this != null);
-    let start: isize = 0;
-    let len: isize = this.length;
+    var start: isize = 0;
+    var len: isize = this.length;
     while (start < len && isWhiteSpaceOrLineTerminator(load<u16>(this.ptr + (start << 1))))
       ++start;
     if (!start)
@@ -164,7 +164,7 @@ export class String {
 
   trimRight(): String {
     assert(this != null);
-    let len: isize = this.length;
+    var len: isize = this.length;
     while (len > 0 && isWhiteSpaceOrLineTerminator(load<u16>(this.ptr + (len << 1))))
       --len;
     if (len <= 0)
diff --git a/std/portable.d.ts b/std/portable.d.ts
index e7b20cd6..3f03257c 100644
--- a/std/portable.d.ts
+++ b/std/portable.d.ts
@@ -116,7 +116,7 @@ declare function store<T = u8>(offset: usize, value: T): void;
 declare function unreachable(): any; // sic
 
 /** Changes the type of a value to another one. Useful for casting class instances to their pointer values and vice-versa. */
-declare function changetype<T1,T2>(value: T1): T2;
+declare function changetype<T>(value: any): T;
 /** Traps if the specified value evaluates to `false`. */
 declare function assert(isTrue: bool, message?: string): void;
 /** Parses an integer string to a 64-bit float. */