Type Members

1.  sealed abstract class AnyFieldDef extends MemberDef
2.  sealed case class Apply(flags: ApplyFlags, receiver: Tree, method: MethodIdent, args: List[Tree])(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable

   Apply an instance method with dynamic dispatch (the default).

3.  sealed case class ApplyDynamicImport(flags: ApplyFlags, className: ClassName, method: MethodIdent, args: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable

   Apply a static method via dynamic import.

4.  final class ApplyFlags extends AnyVal
5.  sealed case class ApplyStatic(flags: ApplyFlags, className: ClassName, method: MethodIdent, args: List[Tree])(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable

   Apply a static method.

6.  sealed case class ApplyStatically(flags: ApplyFlags, receiver: Tree, className: ClassName, method: MethodIdent, args: List[Tree])(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable

   Apply an instance method with static dispatch (e.g., super calls).

7.  sealed case class ApplyTypedClosure(flags: ApplyFlags, fun: Tree, args: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable

   Apply a typed closure

   Apply a typed closure

   The given fun must have a closure type.

   The arguments' types must match (be subtypes of) the parameter types of the closure type.

   The tpe of this node is the result type of the closure type, or nothing if the latter is nothing.

   Evaluation steps are as follows:

   1. Let funV be the result of evaluating fun. 2. If funV is nullClosure, trigger an NPE undefined behavior. 3. Let argsV be the result of evaluating args, in order. 4. Invoke funV with arguments argsV, and return the result.
8.  sealed case class ArraySelect(array: Tree, index: Tree)(tpe: Type)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
9.  sealed case class ArrayValue(typeRef: ArrayTypeRef, elems: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable
10.  sealed case class AsInstanceOf(expr: Tree, tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable
11.  sealed case class Assign(lhs: AssignLhs, rhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable
12.  sealed trait AssignLhs extends Tree
13.  sealed case class BinaryOp(op: Code, lhs: Tree, rhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    Binary operation.

    Binary operation.

    All binary operations follow common evaluation steps:

    1. Let lhsValue be the result of evaluating lhs. 2. Let rhsValue be the result of evaluating rhs. 3. Perform an operation that depends on op, lhsValue and rhsValue.

    Unless lhsValue throws, rhsValue will therefore always be evaluated, even if the operation op would throw based only on lhsValue.

    The integer dividing operators (Int_/, Int_%, Long_/ and Long_%) throw an ArithmeticException when their right-hand-side is 0. That exception is not subject to undefined behavior.

    String_charAt throws a StringIndexOutOfBoundsException.

    The Class_x operations take a jl.Class! as lhs, i.e., a non-nullable jl.Class. Class_isAssignableFrom also takes a jl.Class! as rhs.

    • Class_isInstance and Class_isAssignableFrom are pure.
    • Class_cast throws a CCE if its second argument is non-null and not an instance of the class represented by its first argument.
    • Class_newArray throws a NegativeArraySizeException if its second argument is negative and an IllegalArgumentException if its first argument is classOf[Unit].

    Otherwise, binary operations preserve pureness.

14.  sealed class Block extends Tree
15.  sealed case class BooleanLiteral(value: Boolean)(implicit pos: Position) extends Tree with Literal with Product with Serializable
16.  sealed case class ByteLiteral(value: Byte)(implicit pos: Position) extends Tree with Literal with Product with Serializable
17.  sealed case class CharLiteral(value: Char)(implicit pos: Position) extends Tree with Literal with Product with Serializable
18.  final class ClassDef extends IRNode
19.  sealed case class ClassIdent(name: ClassName)(implicit pos: Position) extends IRNode with Product with Serializable
20.  sealed case class ClassOf(typeRef: TypeRef)(implicit pos: Position) extends Tree with Literal with Product with Serializable
21.  sealed case class Closure(flags: ClosureFlags, captureParams: List[ParamDef], params: List[ParamDef], restParam: Option[ParamDef], resultType: Type, body: Tree, captureValues: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable

    Closure with explicit captures.

    Closure with explicit captures.

    If flags.typed is true, this is a typed closure with a ClosureType. In that case, flags.arrow must be true, and restParam must be None. Typed closures cannot be passed to JavaScript code. This is enforced at the type system level, since ClosureTypes are not subtypes of AnyType. The only meaningful operation one can perform on a typed closure is to call it using ApplyTypedClosure.

    If flags.typed is false, this is a JavaScript closure with type AnyNotNullType. In that case, the ptpe or all params and resultType must all be AnyType.

    If flags.arrow is true, the closure is an Arrow Function (=>), which does not have a this parameter, and cannot be constructed (called with new). If false, it is a regular Function (function), which does have a this parameter of type AnyType. Typed closures are always Arrow functions, since they do not have a this parameter.

    If flags.async is true, it is an async closure. Async closures return a Promise of their body, and can contain JSAwait nodes. flags.typed and flags.async cannot both be true.

22.  final class ClosureFlags extends AnyVal
23.  sealed case class CreateJSClass(className: ClassName, captureValues: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable

    Creates a JavaScript class value.

    Creates a JavaScript class value.

    className

    Reference to the ClassDef for the class definition, which must have jsClassCaptures.nonEmpty

    captureValues

    Actual values for the captured parameters (in the ClassDef's jsClassCaptures.get)

24.  sealed case class Debugger()(implicit pos: Position) extends Tree with Product with Serializable
25.  sealed case class DoubleLiteral(value: Double)(implicit pos: Position) extends Tree with Literal with Product with Serializable
26.  sealed case class FieldDef(flags: MemberFlags, name: FieldIdent, originalName: OriginalName, ftpe: Type)(implicit pos: Position) extends AnyFieldDef with Product with Serializable
27.  sealed case class FieldIdent(name: FieldName)(implicit pos: Position) extends IRNode with Product with Serializable
28.  sealed case class FloatLiteral(value: Float)(implicit pos: Position) extends Tree with Literal with Product with Serializable
29.  sealed case class ForIn(obj: Tree, keyVar: LocalIdent, keyVarOriginalName: OriginalName, body: Tree)(implicit pos: Position) extends Tree with Product with Serializable
30.  sealed abstract class IRNode extends AnyRef

    Base class for all nodes in the IR.

    Base class for all nodes in the IR.

    Usually, one of the direct subclasses of IRNode should be used instead.

31.  sealed case class If(cond: Tree, thenp: Tree, elsep: Tree)(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable
32.  sealed case class IntLiteral(value: Int)(implicit pos: Position) extends Tree with MatchableLiteral with Product with Serializable
33.  sealed case class IsInstanceOf(expr: Tree, testType: Type)(implicit pos: Position) extends Tree with Product with Serializable
34.  sealed case class JSArrayConstr(items: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable
35.  sealed case class JSAwait(arg: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    await arg.

    await arg.

    This is directly equivalent to a JavaScript await expression.

    If used directly within a Closure node with the async flag, this node is always valid. However, when used anywhere else, it is an "orphan" await. Orphan awaits only link when targeting WebAssembly.

    This is not a UnaryOp because of the above strict scoping rule. For example, unless it is orphan to begin with, it is not safe to pull this node out of or into an intervening closure, contrary to UnaryOps.

36.  sealed case class JSBinaryOp(op: Code, lhs: Tree, rhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    JavaScript binary operation.

37.  sealed case class JSConstructorBody(beforeSuper: List[Tree], superCall: JSSuperConstructorCall, afterSuper: List[Tree])(implicit pos: Position) extends IRNode with Product with Serializable
38.  sealed case class JSConstructorDef(flags: MemberFlags, args: List[ParamDef], restParam: Option[ParamDef], body: JSConstructorBody)(optimizerHints: OptimizerHints, version: Version)(implicit pos: Position) extends MemberDef with VersionedMemberDef with Product with Serializable
39.  sealed case class JSDelete(qualifier: Tree, item: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    delete qualifier[item]

40.  sealed case class JSFieldDef(flags: MemberFlags, name: Tree, ftpe: Type)(implicit pos: Position) extends AnyFieldDef with Product with Serializable
41.  sealed case class JSFunctionApply(fun: Tree, args: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable
42.  sealed case class JSGlobalRef(name: String)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
43.  sealed case class JSImportCall(arg: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    JavaScript dynamic import of the form import(arg).

    JavaScript dynamic import of the form import(arg).

    This form is its own node, rather than using something like

    JSFunctionApply(JSImport())

    because import is not a first-class term in JavaScript. ImportCall is a dedicated syntactic form that cannot be dissociated.

44.  sealed case class JSImportMeta()(implicit pos: Position) extends Tree with Product with Serializable

    JavaScript meta-property import.meta.

    JavaScript meta-property import.meta.

    This form is its own node, rather than using something like

    JSSelect(JSImport(), StringLiteral("meta"))

    because import is not a first-class term in JavaScript. import.meta is a dedicated syntactic form that cannot be dissociated.

45.  sealed case class JSMethodApply(receiver: Tree, method: Tree, args: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable
46.  sealed case class JSMethodDef(flags: MemberFlags, name: Tree, args: List[ParamDef], restParam: Option[ParamDef], body: Tree)(optimizerHints: OptimizerHints, version: Version)(implicit pos: Position) extends JSMethodPropDef with Product with Serializable
47.  sealed abstract class JSMethodPropDef extends MemberDef with VersionedMemberDef
48.  sealed abstract class JSNativeLoadSpec extends AnyRef

    Loading specification for a native JS class or object.

49.  sealed case class JSNativeMemberDef(flags: MemberFlags, name: MethodIdent, jsNativeLoadSpec: JSNativeLoadSpec)(implicit pos: Position) extends MemberDef with Product with Serializable
50.  sealed case class JSNew(ctor: Tree, args: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable
51.  sealed case class JSNewTarget()(implicit pos: Position) extends Tree with Product with Serializable

    JavaScript meta-property new.target.

    JavaScript meta-property new.target.

    This form is its own node, rather than using something like

    JSSelect(JSNew(), StringLiteral("target"))

    because new is not a first-class term in JavaScript. new.target is a dedicated syntactic form that cannot be dissociated.

52.  sealed case class JSObjectConstr(fields: List[(Tree, Tree)])(implicit pos: Position) extends Tree with Product with Serializable
53.  sealed case class JSPrivateSelect(qualifier: Tree, field: FieldIdent)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
54.  sealed case class JSPropertyDef(flags: MemberFlags, name: Tree, getterBody: Option[Tree], setterArgAndBody: Option[(ParamDef, Tree)])(version: Version)(implicit pos: Position) extends JSMethodPropDef with Product with Serializable
55.  sealed case class JSSelect(qualifier: Tree, item: Tree)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
56.  sealed case class JSSpread(items: Tree)(implicit pos: Position) extends IRNode with TreeOrJSSpread with Product with Serializable

    ...items, the "spread" operator of ECMAScript 6.

    ...items, the "spread" operator of ECMAScript 6.

    items

    An Array whose items will be spread (not an arbitrary iterable)

57.  sealed case class JSSuperConstructorCall(args: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable

    Super constructor call in the constructor of a non-native JS class.

    Super constructor call in the constructor of a non-native JS class.

    Exactly one such node must appear in the constructor of a non-native JS class, at the top-level (possibly as a direct child of a top-level Block). Any other use of this node is invalid.

    Statements before this node, as well as the args, cannot contain any This() node. Statements after this node can use This().

    After the execution of this node, it is guaranteed that all fields declared in the current class have been created and initialized. Up to that point, accessing any field declared in this class (e.g., through an overridden method called from the super constructor) is undefined behavior.

    All in all, the shape of a constructor is therefore:

    {
      statementsNotUsingThis();
      JSSuperConstructorCall(...argsNotUsingThis);
      statementsThatMayUseThis()
    }

    which currently translates to something of the following shape:

    {
      statementsNotUsingThis();
      super(...argsNotUsingThis);
      this.privateField1 = 0;
      this["publicField2"] = false;
      statementsThatMayUseThis()
    }

58.  sealed case class JSSuperMethodCall(superClass: Tree, receiver: Tree, method: Tree, args: List[TreeOrJSSpread])(implicit pos: Position) extends Tree with Product with Serializable

    Calls a method inherited from the given superClass on receiver.

    Calls a method inherited from the given superClass on receiver.

    Intuitively, this corresponds to

    superClass.prototype[method].call(receiver, ...args)

    but retains more structure at the IR level than using an explicit encoding of the above expression.

    Given the non-native JS classes

    class Bar extends js.Object
    class Foo extends Bar

    The node

    JSSuperBrackerCall(LoadJSConstructor(ClassName("Bar")), receiver, method, args)

    which is printed as

    super(constructorOf[Bar])::receiver[method](...args)

    has the following semantics:

    Bar.prototype[method].call(receiver, ...args)

    If this happens to be located in an instance method of Foo, *and* receiver happens to be This(), this is equivalent to the ES6 statement

    super[method](...args)

59.  sealed case class JSSuperSelect(superClass: Tree, receiver: Tree, item: Tree)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable

    Selects a property inherited from the given superClass on receiver.

    Selects a property inherited from the given superClass on receiver.

    Given the non-native JS classes

    class Bar extends js.Object
    class Foo extends Bar

    The node

    JSSuperBrackerSelect(LoadJSConstructor(ClassName("Bar")), qualifier, item)

    which is printed as

    super(constructorOf[Bar])::qualifier[item]

    has the semantics of an ES6 super reference

    super[item]

    as if it were in an instance method of Foo with qualifier as the this value.

60.  sealed case class JSTypeOfGlobalRef(globalRef: JSGlobalRef)(implicit pos: Position) extends Tree with Product with Serializable
61.  sealed case class JSUnaryOp(op: Code, lhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable

    JavaScript unary operation.

62.  sealed case class Labeled(label: LabelName, tpe: Type, body: Tree)(implicit pos: Position) extends Tree with Product with Serializable
63.  sealed case class LinkTimeProperty(name: String)(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable
64.  sealed trait Literal extends Tree

    Marker for literals.

    Marker for literals. Literals are always pure.

    All Literals can be compared for equality. The equality does not take the pos into account.

65.  sealed case class LoadJSConstructor(className: ClassName)(implicit pos: Position) extends Tree with Product with Serializable

    Loads the constructor of a JS class (native or not).

    Loads the constructor of a JS class (native or not).

    className must represent a non-trait JS class (native or not).

    This is used typically to instantiate a JS class, and most importantly if it is a non-native JS class. Given the class

    class Foo(x: Int) extends js.Object

    The instantiation new Foo(1) would be represented as

    JSNew(LoadJSConstructor(ClassName("Foo")), List(IntLiteral(1)))

    This node is also useful to encode o.isInstanceOf[Foo]:

    JSBinaryOp(instanceof, o, LoadJSConstructor(ClassName("Foo")))

    If Foo is non-native, the presence of this node makes it instantiable, and therefore reachable.

66.  sealed case class LoadJSModule(className: ClassName)(implicit pos: Position) extends Tree with Product with Serializable

    Like LoadModule but for a JS module class.

67.  sealed case class LoadModule(className: ClassName)(implicit pos: Position) extends Tree with Product with Serializable
68.  sealed case class LocalIdent(name: LocalName)(implicit pos: Position) extends IRNode with Product with Serializable
69.  sealed case class LongLiteral(value: Long)(implicit pos: Position) extends Tree with Literal with Product with Serializable
70.  sealed case class Match(selector: Tree, cases: List[(List[MatchableLiteral], Tree)], default: Tree)(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable

    A break-free switch (without fallthrough behavior).

    A break-free switch (without fallthrough behavior).

    Unlike a JavaScript switch, it can be used in expression position. It supports alternatives explicitly (hence the List[MatchableLiteral] in cases), whereas in a switch one would use the fallthrough behavior to implement alternatives. (This is not a pattern matching construct like in Scala.)

    The selector must be either an int (IntType) or a java.lang.String. The cases can be any MatchableLiteral, even if they do not make sense for the type of the selecter (they simply will never match).

    Because +0.0 === -0.0 in JavaScript, and because those semantics are used in a JS switch, we have to prevent the selector from ever being -0.0. Otherwise, it would be matched by a case IntLiteral(0). At the same time, we must allow at least int and java.lang.String to support all switchable matches from Scala. Since the latter two have no common super type that does not allow -0.0, we really have to special-case those two types.

    This is also why we restrict MatchableLiterals to IntLiteral, StringLiteral and Null. Allowing more cases would only make IR checking more complicated, without bringing any added value.

71.  sealed trait MatchableLiteral extends Tree with Literal

    Marker for literals that can be used in a Match case.

    Marker for literals that can be used in a Match case.

    Matchable literals are:

    • IntLiteral
    • StringLiteral
    • Null

    See Match for the rationale about that specific set.

72.  sealed abstract class MemberDef extends IRNode

    Any member of a ClassDef.

    Any member of a ClassDef.

    Partitioned into AnyFieldDef, MethodDef, JSConstructorDef and JSMethodPropDef.

73.  final class MemberFlags extends AnyVal
74.  final class MemberNamespace extends AnyVal
75.  sealed case class MethodDef(flags: MemberFlags, name: MethodIdent, originalName: OriginalName, args: List[ParamDef], resultType: Type, body: Option[Tree])(optimizerHints: OptimizerHints, version: Version)(implicit pos: Position) extends MemberDef with VersionedMemberDef with Product with Serializable
76.  sealed case class MethodIdent(name: MethodName)(implicit pos: Position) extends IRNode with Product with Serializable
77.  sealed case class New(className: ClassName, ctor: MethodIdent, args: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable
78.  sealed case class NewArray(typeRef: ArrayTypeRef, length: Tree)(implicit pos: Position) extends Tree with Product with Serializable
79.  sealed case class NewLambda(descriptor: Descriptor, fun: Tree)(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable

    New lambda instance of a SAM class.

    New lambda instance of a SAM class.

    Functionally, a NewLambda is equivalent to an instance of an anonymous class with the following shape:

    val funV: ((...Ts) => R)! = fun;
    (new superClass with interfaces {
      def <this>() = this.superClass::<init>()
      def methodName(...args: Ts): R = funV(...args)
    }): tpe

    where superClass, interfaces, methodName, Ts and R are taken from the descriptor. Ts and R are the paramTypes and resultType of the descriptor. They are required because there is no one-to-one mapping between TypeRefs and Types, and we want the shape of the class to be a deterministic function of the descriptor.

    The fun must have type ((...Ts) => R)!.

    Intuitively, tpe must be a supertype of superClass! & ...interfaces!. Since our type system does not have intersection types, in practice this means that there must exist C ∈ { superClass } ∪ interfaces such that tpe is a supertype of C!.

    The uniqueness of the anonymous class and its run-time class name are not guaranteed.

80.  sealed case class Null()(implicit pos: Position) extends Tree with MatchableLiteral with Product with Serializable
81.  final class OptimizerHints extends AnyVal
82.  sealed case class ParamDef(name: LocalIdent, originalName: OriginalName, ptpe: Type, mutable: Boolean)(implicit pos: Position) extends IRNode with Product with Serializable
83.  sealed case class RecordSelect(record: Tree, field: SimpleFieldIdent)(tpe: Type)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
84.  sealed case class RecordValue(tpe: RecordType, elems: List[Tree])(implicit pos: Position) extends Tree with Product with Serializable
85.  sealed case class Return(expr: Tree, label: LabelName)(implicit pos: Position) extends Tree with Product with Serializable
86.  sealed case class Select(qualifier: Tree, field: FieldIdent)(tpe: Type)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
87.  sealed case class SelectJSNativeMember(className: ClassName, member: MethodIdent)(implicit pos: Position) extends Tree with Product with Serializable
88.  sealed case class SelectStatic(field: FieldIdent)(tpe: Type)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
89.  sealed case class ShortLiteral(value: Short)(implicit pos: Position) extends Tree with Literal with Product with Serializable
90.  sealed case class SimpleFieldIdent(name: SimpleFieldName)(implicit pos: Position) extends IRNode with Product with Serializable
91.  sealed case class Skip()(implicit pos: Position) extends Tree with Product with Serializable
92.  sealed case class StoreModule()(implicit pos: Position) extends Tree with Product with Serializable
93.  sealed case class StringLiteral(value: String)(implicit pos: Position) extends Tree with MatchableLiteral with Product with Serializable
94.  sealed abstract class TopLevelExportDef extends IRNode
95.  sealed case class TopLevelFieldExportDef(moduleID: String, exportName: String, field: FieldIdent)(implicit pos: Position) extends TopLevelExportDef with Product with Serializable
96.  sealed case class TopLevelJSClassExportDef(moduleID: String, exportName: String)(implicit pos: Position) extends TopLevelExportDef with Product with Serializable
97.  sealed case class TopLevelMethodExportDef(moduleID: String, methodDef: JSMethodDef)(implicit pos: Position) extends TopLevelExportDef with Product with Serializable
98.  sealed case class TopLevelModuleExportDef(moduleID: String, exportName: String)(implicit pos: Position) extends TopLevelExportDef with Product with Serializable

    Export for a top-level object.

    Export for a top-level object.

    This exports the singleton instance of the containing module class. The instance is initialized during ES module instantiation.

99.  sealed case class Transient(value: Value)(implicit pos: Position) extends Tree with Product with Serializable

    A transient node for custom purposes.

    A transient node for custom purposes.

    A transient node is never a valid input to the Serializers nor to the linker, but can be used in a transient state for internal purposes.

    value

    The payload of the transient node, without any specified meaning.

100.  sealed abstract class Tree extends IRNode with TreeOrJSSpread

     Node for a statement or expression in the IR.

101.  sealed trait TreeOrJSSpread extends IRNode

     Either a Tree or a JSSpread.

     Either a Tree or a JSSpread.

     This is the type of actual arguments to JS applications.

102.  sealed case class TryCatch(block: Tree, errVar: LocalIdent, errVarOriginalName: OriginalName, handler: Tree)(tpe: Type)(implicit pos: Position) extends Tree with Product with Serializable
103.  sealed case class TryFinally(block: Tree, finalizer: Tree)(implicit pos: Position) extends Tree with Product with Serializable
104.  sealed case class UnaryOp(op: Code, lhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable

     Unary operation.

     Unary operation.

     All unary operations follow common evaluation steps:

     1. Let lhsValue be the result of evaluating lhs. 2. Perform an operation that depends on op and lhsValue.

     The Class_x operations take a jl.Class! argument, i.e., a non-nullable jl.Class.

     Likewise, Array_length, GetClass, Clone and UnwrapFromThrowable take arguments of non-nullable types.

     CheckNotNull throws NPEs subject to UB.

     Throw always throws, obviously.

     Clone and WrapAsThrowable are side-effect-free but not pure.

     Otherwise, unary operations preserve pureness.

105.  sealed case class Undefined()(implicit pos: Position) extends Tree with Literal with Product with Serializable
106.  sealed case class VarDef(name: LocalIdent, originalName: OriginalName, vtpe: Type, mutable: Boolean, rhs: Tree)(implicit pos: Position) extends Tree with Product with Serializable
107.  sealed case class VarRef(name: LocalName)(tpe: Type)(implicit pos: Position) extends Tree with AssignLhs with Product with Serializable
108.  sealed trait VersionedMemberDef extends MemberDef
109.  sealed case class While(cond: Tree, body: Tree)(implicit pos: Position) extends Tree with Product with Serializable