swift-mirror/lib/AST/Expr.cpp

//===--- Expr.cpp - Swift Language Expression ASTs ------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
//  This file implements the Expr class and subclasses.
//
//===----------------------------------------------------------------------===//

#include "swift/AST/Expr.h"
#include "swift/AST/ASTVisitor.h"
#include "swift/AST/Types.h"
#include "swift/AST/ASTContext.h"
#include "swift/AST/PrettyStackTrace.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/Support/raw_ostream.h"
using namespace swift;

//===----------------------------------------------------------------------===//
// Expr methods.
//===----------------------------------------------------------------------===//

// Only allow allocation of Stmts using the allocator in ASTContext.
void *Expr::operator new(size_t Bytes, ASTContext &C,
                         unsigned Alignment) throw() {
  return C.Allocate(Bytes, Alignment);
}

// Helper functions to verify statically whether the getSourceRange()
// function has been overridden.
typedef const char (&TwoChars)[2];

template<typename Class> 
inline char checkSourceRangeType(SourceRange (Class::*)() const);

inline TwoChars checkSourceRangeType(SourceRange (Expr::*)() const);

SourceRange Expr::getSourceRange() const {
  switch (Kind) {
#define EXPR(ID, PARENT) \
case ExprKind::ID: \
static_assert(sizeof(checkSourceRangeType(&ID##Expr::getSourceRange)) == 1, \
              #ID "Expr is missing getSourceRange()"); \
return cast<ID##Expr>(this)->getSourceRange();
#include "swift/AST/ExprNodes.def"
  }
  
  llvm_unreachable("expression type not handled!");
}

/// getLoc - Return the caret location of the expression.
SourceLoc Expr::getLoc() const {
  switch (Kind) {
#define EXPR(ID, PARENT) \
  case ExprKind::ID: \
    if (&Expr::getLoc != &ID##Expr::getLoc) \
      return cast<ID##Expr>(this)->getLoc(); \
    break;
#include "swift/AST/ExprNodes.def"
  }

  return getStartLoc();
}

//===----------------------------------------------------------------------===//
// Support methods for Exprs.
//===----------------------------------------------------------------------===//

/// getNumArgs - Return the number of arguments that this closure expr takes.
/// This is the length of the ArgList.
unsigned ClosureExpr::getNumArgs() const {
  Type Input = getType()->getAs<FunctionType>()->Input;
  
  if (TupleType *TT = Input->getAs<TupleType>())
    return TT->Fields.size();
  return 1;  
}

APInt IntegerLiteralExpr::getValue() const {
  assert(!getType().isNull() && "Semantic analysis has not completed");
  unsigned BitWidth = getType()->castTo<BuiltinIntegerType>()->getBitWidth();
  
  llvm::APInt Value(BitWidth, 0);
  bool Error = getText().getAsInteger(0, Value);
  assert(!Error && "Invalid IntegerLiteral formed"); (void)Error;
  assert(Value.getActiveBits() <= BitWidth && "Value too large for size");
  if (Value.getBitWidth() != BitWidth)
    Value = Value.zextOrTrunc(BitWidth);
  return Value;
}

llvm::APFloat FloatLiteralExpr::getValue() const {
  assert(!getType().isNull() && "Semantic analysis has not completed");
  
  APFloat Val(getType()->castTo<BuiltinFloatType>()->getAPFloatSemantics());
  APFloat::opStatus Res =
    Val.convertFromString(getText(), llvm::APFloat::rmNearestTiesToEven);
  assert(Res != APFloat::opInvalidOp && "Sema didn't reject invalid number");
  (void)Res;
  return Val;
}

SequenceExpr *SequenceExpr::create(ASTContext &ctx, ArrayRef<Expr*> elements) {
  void *Buffer = ctx.Allocate(sizeof(SequenceExpr) +
                              elements.size() * sizeof(Expr*),
                              Expr::Alignment);
  return ::new(Buffer) SequenceExpr(elements);
}

SourceRange TupleExpr::getSourceRange() const {
  SourceLoc Start = LParenLoc;
  if (!Start.isValid())
    Start = getElement(0)->getStartLoc();

  SourceLoc End = RParenLoc;
  if (!End.isValid())
    End = getElement(getNumElements() - 1)->getEndLoc();
  
  return SourceRange(Start, End);
}

SourceRange FuncExpr::getSourceRange() const {
  return SourceRange(FuncLoc, Body->getEndLoc());
}

/// Returns the result type of the function defined by the body.  For
/// an uncurried function, this is just the normal result type; for a
/// curried function, however, this is the result type of the
/// uncurried part.
///
/// Examples:
///   func(x : int) -> ((y : int) -> (int -> int))
///     The body result type is '((y : int) -> (int -> int))'.
///   func(x : int) -> (y : int) -> (int -> int)
///     The body result type is '(int -> int)'.
Type FuncExpr::getBodyResultType() const {
  Type ty = cast<FunctionType>(getType())->Result;
  while (FunctionType *fn = dyn_cast<FunctionType>(ty)) {
    ty = fn->Result;
  }
  return ty;
}

static ValueDecl *getCalledValue(Expr *E) {
  if (DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(E))
    return DRE->getDecl();

  if (ParenExpr *PE = dyn_cast<ParenExpr>(E))
    return getCalledValue(PE->getSubExpr());

  return nullptr;
}

ValueDecl *ApplyExpr::getCalledValue() const {
  return ::getCalledValue(Fn);
}

//===----------------------------------------------------------------------===//
//  Type Conversion Ranking
//===----------------------------------------------------------------------===//

/// convertTupleToTupleType - Given an expression that has tuple type, convert
/// it to have some other tuple type.
///
/// The caller gives us a list of the expressions named arguments and a count of
/// tuple elements for E in the IdentList+NumIdents array.  DestTy specifies the
/// type to convert to, which is known to be a TupleType.
static Expr::ConversionRank 
getTupleToTupleTypeConversionRank(const Expr *E, unsigned NumExprElements,
                                  TupleType *DestTy) {
  // If the tuple expression or destination type have named elements, we
  // have to match them up to handle the swizzle case for when:
  //   (.y = 4, .x = 3)
  // is converted to type:
  //   (.x = int, .y = int)
  SmallVector<Identifier, 8> IdentList(NumExprElements);
  
  // Check to see if this conversion is ok by looping over all the destination
  // elements and seeing if they are provided by the input.
  
  // Keep track of which input elements are used.
  SmallVector<bool, 16> UsedElements(NumExprElements);
  SmallVector<int, 16>  DestElementSources(DestTy->Fields.size(), -1);

  if (TupleType *ETy = E->getType()->getAs<TupleType>()) {
    assert(ETy->Fields.size() == NumExprElements && "Expr #elements mismatch!");
    { unsigned i = 0;
    for (const TupleTypeElt &Elt : ETy->Fields)
      IdentList[i++] = Elt.Name;
    }
  
    // First off, see if we can resolve any named values from matching named
    // inputs.
    for (unsigned i = 0, e = DestTy->Fields.size(); i != e; ++i) {
      const TupleTypeElt &DestElt = DestTy->Fields[i];
      // If this destination field is named, first check for a matching named
      // element in the input, from any position.
      if (DestElt.Name.empty()) continue;
      
      int InputElement = -1;
      for (unsigned j = 0; j != NumExprElements; ++j)
        if (IdentList[j] == DestElt.Name) {
          InputElement = j;
          break;
        }
      if (InputElement == -1) continue;
      
      DestElementSources[i] = InputElement;
      UsedElements[InputElement] = true;
    }
  }
  
  // Next step, resolve (in order) unmatched named results and unnamed results
  // to any left-over unnamed input.
  unsigned NextInputValue = 0;
  for (unsigned i = 0, e = DestTy->Fields.size(); i != e; ++i) {
    // If we already found an input to satisfy this output, we're done.
    if (DestElementSources[i] != -1) continue;
    
    // Scan for an unmatched unnamed input value.
    while (1) {
      // If we didn't find any input values, we ran out of inputs to use.
      if (NextInputValue == NumExprElements)
        break;
      
      // If this input value is unnamed and unused, use it!
      if (!UsedElements[NextInputValue] && IdentList[NextInputValue].empty())
        break;
      
      ++NextInputValue;
    }
    
    // If we ran out of input values, we either don't have enough sources to
    // fill the dest (as in when assigning (1,2) to (int,int,int), or we ran out
    // and default values should be used.
    if (NextInputValue == NumExprElements) {
      if (DestTy->Fields[i].Init == 0)
        return Expr::CR_Invalid;
        
      // If the default initializer should be used, leave the
      // DestElementSources field set to -2.
      DestElementSources[i] = -2;
      continue;
    }
    
    // Okay, we found an input value to use.
    DestElementSources[i] = NextInputValue;
    UsedElements[NextInputValue] = true;
  }
  
  // If there were any unused input values, we fail.
  for (bool Elt : UsedElements)
    if (!Elt)
      return Expr::CR_Invalid;
  
  // It looks like the elements line up, walk through them and see if the types
  // either agree or can be converted.  If the expression is a TupleExpr, we do
  // this conversion in place.
  const TupleExpr *TE = dyn_cast<TupleExpr>(E);
  if (TE && TE->getNumElements() != 1 &&
      TE->getNumElements() == DestTy->Fields.size()) {
    Expr::ConversionRank CurRank = Expr::CR_Identity;
    
    // The conversion rank of the tuple is the worst case of the conversion rank
    // of each of its elements.
    for (unsigned i = 0, e = DestTy->Fields.size(); i != e; ++i) {
      // Extract the input element corresponding to this destination element.
      unsigned SrcField = DestElementSources[i];
      assert(SrcField != ~0U && "dest field not found?");
      
      // If SrcField is -2, then the destination element just uses its default
      // value.
      if (SrcField == -2U)
        continue;
     
      // Check to see if the src value can be converted to the destination
      // element type.
      Expr *Elt = TE->getElement(SrcField);
      CurRank = std::max(CurRank,
                         Elt->getRankOfConversionTo(DestTy->getElementType(i)));
    }
    return CurRank;
  }
  
  // A tuple-to-tuple conversion of a non-parenthesized tuple is allowed to
  // permute the elements, but cannot perform conversions of each value.
  TupleType *ETy = E->getType()->getAs<TupleType>();
  for (unsigned i = 0, e = DestTy->Fields.size(); i != e; ++i) {
    // Extract the input element corresponding to this destination element.
    unsigned SrcField = DestElementSources[i];
    assert(SrcField != ~0U && "dest field not found?");

    // If SrcField is -2, then the destination element just uses its default
    // value.
    if (SrcField == -2U)
      continue;

    // The element types must match up exactly.
    if (ETy->getElementType(SrcField)->getCanonicalType() !=
        DestTy->getElementType(i)->getCanonicalType())
      return Expr::CR_Invalid;
  }

  return Expr::CR_Identity;
}


/// getConversionRank - Return the conversion rank for converting a value 'E' to
/// type 'ToTy'.
///
/// Note that this code needs to be kept carefully in synch with
/// SemaCoerceBottomUp::convertToType.
static Expr::ConversionRank getConversionRank(const Expr *E, Type DestTy) {
  assert(!DestTy->is<DependentType>() &&
         "Result of conversion can't be dependent");

  // Exact matches are identity conversions.
  if (E->getType()->getCanonicalType() == DestTy->getCanonicalType())
    return Expr::CR_Identity;
  
  // Look through parentheses.
  if (const ParenExpr *PE = dyn_cast<ParenExpr>(E))
    return getConversionRank(PE->getSubExpr(), DestTy);
  
  if (TupleType *TT = DestTy->getAs<TupleType>()) {
    if (const TupleExpr *TE = dyn_cast<TupleExpr>(E))
      return getTupleToTupleTypeConversionRank(TE, TE->getNumElements(),
                                               TT);
    
    // If the is a scalar to tuple conversion, form the tuple and return it.
    int ScalarFieldNo = TT->getFieldForScalarInit();
    if (ScalarFieldNo != -1) {
      // If the destination is a tuple type with at most one element that has no
      // default value, see if the expression's type is convertable to the
      // element type.  This handles assigning 4 to "(a = 4, b : int)".
      return getConversionRank(E, TT->getElementType(ScalarFieldNo));
    }
    
    // If the input is a tuple and the output is a tuple, see if we can convert
    // each element.
    if (TupleType *ETy = E->getType()->getAs<TupleType>())
      return getTupleToTupleTypeConversionRank(E, ETy->Fields.size(), TT);
  }

  // Otherwise, check to see if this is an auto-closure case.  This case happens
  // when we convert an expression E to a function type whose result is E's
  // type.
  if (FunctionType *FT = DestTy->getAs<FunctionType>()) {
    if (getConversionRank(E, FT->Result) == Expr::CR_Invalid)
      return Expr::CR_Invalid;
    
    return Expr::CR_AutoClosure;
  }

  // If the expression has a dependent type or we have some other case, we fail.
  return Expr::CR_Invalid;
}

/// getRankOfConversionTo - Return the rank of a conversion from the current
/// type to the specified type.
Expr::ConversionRank Expr::getRankOfConversionTo(Type DestTy) const {
  return getConversionRank(this, DestTy);
}



//===----------------------------------------------------------------------===//
// Expression Walking
//===----------------------------------------------------------------------===//

namespace {
  /// ExprWalker - This class implements a simple expression walker which
  /// invokes a function pointer on every expression in an AST.  If the function
  /// pointer returns true the walk is terminated.
  class ExprWalker : public ASTVisitor<ExprWalker, Expr*, Stmt*> {
    friend class ASTVisitor<ExprWalker, Expr*, Stmt*>;
    
    typedef ASTVisitor<ExprWalker, Expr*, Stmt*> inherited;
    
    WalkExprType ^ExprFn;
    WalkStmtType ^StmtFn;
    WalkContext WalkCtx;
    
    /// \brief RAII object that sets the parent of the walk context 
    /// appropriately.
    class SetParentRAII {
      WalkContext &WalkCtx;
      llvm::PointerUnion<Expr *, Stmt *> PriorParent;
      
    public:
      template<typename T>
      SetParentRAII(WalkContext &WalkCtx, T *NewParent)
        : WalkCtx(WalkCtx), PriorParent(WalkCtx.Parent) 
      {
        WalkCtx.Parent = NewParent;
      }
      
      ~SetParentRAII() {
        WalkCtx.Parent = PriorParent;
      }
    };
    
    Expr *visit(Expr *E) {
      SetParentRAII SetParent(WalkCtx, E);
      return inherited::visit(E);
    }

    Stmt *visit(Stmt *S) {
      SetParentRAII SetParent(WalkCtx, S);
      return inherited::visit(S);
    }
    
    Expr *visitIntegerLiteralExpr(IntegerLiteralExpr *E) { return E; }
    Expr *visitFloatLiteralExpr(FloatLiteralExpr *E) { return E; }
    Expr *visitDeclRefExpr(DeclRefExpr *E) { return E; }
    Expr *visitOverloadSetRefExpr(OverloadSetRefExpr *E) { return E; }
    Expr *visitUnresolvedDeclRefExpr(UnresolvedDeclRefExpr *E) { return E; }
    Expr *visitUnresolvedMemberExpr(UnresolvedMemberExpr *E) { return E; }
    Expr *visitUnresolvedScopedIdentifierExpr(UnresolvedScopedIdentifierExpr*E){
      return E;
    }

    Expr *visitParenExpr(ParenExpr *E) {
      if (Expr *subExpr = doIt(E->getSubExpr())) {
        E->setSubExpr(subExpr);
        return E;
      }
      return 0;
    }
    Expr *visitTupleExpr(TupleExpr *E) {
      for (unsigned i = 0, e = E->getNumElements(); i != e; ++i)
        if (E->getElement(i)) {
          if (Expr *Elt = doIt(E->getElement(i)))
            E->setElement(i, Elt);
          else
            return 0;
        }
      return E;
    }
    Expr *visitUnresolvedDotExpr(UnresolvedDotExpr *E) {
      if (!E->getBase())
        return E;
      
      if (Expr *E2 = doIt(E->getBase())) {
        E->setBase(E2);
        return E;
      }
      return 0;
    }
    
    Expr *visitLookThroughOneofExpr(LookThroughOneofExpr *E) {
      if (Expr *E2 = doIt(E->getSubExpr())) {
        E->setSubExpr(E2);
        return E;
      }
      return 0;
    }
    
    Expr *visitTupleElementExpr(TupleElementExpr *E) {
      if (Expr *E2 = doIt(E->getBase())) {
        E->setBase(E2);
        return E;
      }
      return 0;
    }
    
    Expr *visitTupleShuffleExpr(TupleShuffleExpr *E) {
      if (Expr *E2 = doIt(E->getSubExpr())) {
        E->setSubExpr(E2);
        return E;
      }
      return 0;
    }
    
    Expr *visitLoadExpr(LoadExpr *E) {
      if (Expr *E2 = doIt(E->getSubExpr())) {
        E->setSubExpr(E2);
        return E;
      }
      return 0;
    }
  
    Expr *visitSequenceExpr(SequenceExpr *E) {
      for (unsigned i = 0, e = E->getNumElements(); i != e; ++i)
        if (Expr *Elt = doIt(E->getElement(i)))
          E->setElement(i, Elt);
        else
          return 0;
      return E;
    }
    
    Expr *visitFuncExpr(FuncExpr *E) {
      if (BraceStmt *S = cast_or_null<BraceStmt>(doIt(E->getBody()))) {
        E->setBody(S);
        return E;
      }
      return 0;
    }
    
    Expr *visitClosureExpr(ClosureExpr *E) {
      if (Expr *E2 = doIt(E->getInput())) {
        E->setInput(E2);
        return E;
      }
      return 0;
    }
    
    Expr *visitAnonClosureArgExpr(AnonClosureArgExpr *E) { return E; }

    Expr *visitApplyExpr(ApplyExpr *E) {
      Expr *E2 = doIt(E->getFn());
      if (E2 == 0) return 0;
      E->setFn(E2);
      
      E2 = doIt(E->getArg());
      if (E2 == 0) return 0;
      E->setArg(E2);
      return E;      
    }

    Expr *visitCallExpr(CallExpr *E) {
      return visitApplyExpr(E);
    }

    Expr *visitUnaryExpr(UnaryExpr *E) {
      return visitApplyExpr(E);
    }

    Expr *visitBinaryExpr(BinaryExpr *E) {
      // Visit the arguments to the tuple, but visit the operator in
      // infix order.
      TupleExpr *Arg = E->getArgTuple();
      assert(Arg->getNumElements() == 2);
      Expr *E2 = doIt(Arg->getElement(0));
      if (E2 == 0) return 0;
      Arg->setElement(0, E2);

      E2 = doIt(E->getFn());
      if (E2 == 0) return 0;
      E->setFn(E2);
      
      E2 = doIt(Arg->getElement(1));
      if (E2 == 0) return 0;
      Arg->setElement(1, E2);
      return E;
    }

    Expr *visitConstructorCallExpr(ConstructorCallExpr *E) {
      return visitApplyExpr(E);
    }

    Expr *visitDotSyntaxCallExpr(DotSyntaxCallExpr *E) {
      return visitApplyExpr(E);
    }
    
    Expr *visitDotSyntaxPlusFuncUseExpr(DotSyntaxPlusFuncUseExpr *E) {
      Expr *E2 = doIt(E->getBaseExpr());
      if (E2 == 0) return 0;
      E->setBaseExpr(E2);
      
      E2 = doIt(E->getPlusFuncExpr());
      if (E2 == 0) return 0;
      E->setPlusFuncExpr(cast<DeclRefExpr>(E2));
      return E;      
    }    

    Stmt *visitSemiStmt(SemiStmt *SS) {
      return SS;
    }
    
    Stmt *visitAssignStmt(AssignStmt *AS) {
      if (Expr *E = doIt(AS->getDest()))
        AS->setDest(E);
      else
        return 0;

      if (Expr *E = doIt(AS->getSrc()))
        AS->setSrc(E);
      else
        return 0;
      return AS;
    }
    
    Stmt *visitBraceStmt(BraceStmt *BS) {
      for (unsigned i = 0, e = BS->getNumElements(); i != e; ++i) {
        if (Expr *SubExpr = BS->getElement(i).dyn_cast<Expr*>()) {
          if (Expr *E2 = doIt(SubExpr))
            BS->setElement(i, E2);
          else
            return 0;
          continue;
        }
        
        if (Stmt *S = BS->getElement(i).dyn_cast<Stmt*>()) {
          if (Stmt *S2 = doIt(S))
            BS->setElement(i, S2);
          else
            return 0;
          continue;
        }

        if (visitDecl(BS->getElement(i).get<Decl*>()))
          return 0;
      }
      
      return BS;
    }

    Stmt *visitReturnStmt(ReturnStmt *RS) {
      if (Expr *E = doIt(RS->getResult()))
        RS->setResult(E);
      else
        return 0;
      return RS;
    }
    
    Stmt *visitIfStmt(IfStmt *IS) {
      if (Expr *E2 = doIt(IS->getCond()))
        IS->setCond(E2);
      else
        return 0;
      
      if (Stmt *S2 = doIt(IS->getThenStmt()))
        IS->setThenStmt(S2);
      else
        return 0;
      
      if (IS->getElseStmt()) {
        if (Stmt *S2 = doIt(IS->getElseStmt()))
          IS->setElseStmt(S2);
        else
          return 0;
      }
      return IS;
    }
    
    Stmt *visitWhileStmt(WhileStmt *WS) {
      if (Expr *E2 = doIt(WS->getCond()))
        WS->setCond(E2);
      else
        return 0;
      
      if (Stmt *S2 = doIt(WS->getBody()))
        WS->setBody(S2);
      else
        return 0;
      return WS;
    }

    /// Returns true on failure.
    bool visitDecl(Decl *D) {
      if (ValueDecl *VD = dyn_cast<ValueDecl>(D)) {
        if (Expr *Init = VD->getInit()) {
#ifndef NDEBUG
          PrettyStackTraceDecl debugStack("walking into initializer for", VD);
#endif
          if (Expr *E2 = doIt(Init))
            VD->setInit(E2);
          else
            return true;
        }
      } else if (ExtensionDecl *ED = dyn_cast<ExtensionDecl>(D)) {
        for (Decl *M : ED->getMembers()) {
          if (visitDecl(M))
            return true;
        }
      }
      return false;
    }
       
  public:
    ExprWalker(WalkExprType ^ExprFn, WalkStmtType ^StmtFn)
      : ExprFn(ExprFn), StmtFn(StmtFn) {
    }
    Expr *doIt(Expr *E) {
      // If no visitor function wants to get called before/after the node, just
      // walk into it.
      if (ExprFn == 0)
        return visit(E);
      
      // Try the preorder visitation.  If it returns null, we just skip entering
      // subnodes of this tree.
      Expr *E2 = ExprFn(E, WalkOrder::PreOrder, WalkCtx);
      if (E2 == 0) return E;
      
      if (E) E = visit(E);
      if (E) E = ExprFn(E, WalkOrder::PostOrder, WalkCtx);
      return E;
    }
    Stmt *doIt(Stmt *S) {
      // If no visitor function wants to get called before/after the node, just
      // walk into it.
      if (StmtFn == 0)
        return visit(S);
      
      // Try the preorder visitation.  If it returns null, we just skip entering
      // subnodes of this tree.
      Stmt *S2 = StmtFn(S, WalkOrder::PreOrder, WalkCtx);
      if (S2 == 0) return S;
      
      if (S) S = visit(S);
      if (S) S = StmtFn(S, WalkOrder::PostOrder, WalkCtx);
      return S;
    }
  };
} // end anonymous namespace.

Expr *Expr::walk(WalkExprType ^ExprFn, WalkStmtType ^StmtFn) {
  return ExprWalker(ExprFn, StmtFn).doIt(this);  
}

Stmt *Stmt::walk(WalkExprType ^ExprFn, WalkStmtType ^StmtFn) {
  return ExprWalker(ExprFn, StmtFn).doIt(this);
}



//===----------------------------------------------------------------------===//
// Printing for Expr and all subclasses.
//===----------------------------------------------------------------------===//

namespace {
/// PrintExpr - Visitor implementation of Expr::print.
class PrintExpr : public ExprVisitor<PrintExpr> {
public:
  raw_ostream &OS;
  unsigned Indent;
  
  PrintExpr(raw_ostream &os, unsigned indent) : OS(os), Indent(indent) {
  }
  
  void printRec(Expr *E) {
    Indent += 2;
    if (E)
      visit(E);
    else
      OS.indent(Indent) << "(**NULL EXPRESSION**)";
    Indent -= 2;
  }
  
  /// FIXME: This should use ExprWalker to print children.
  
  void printRec(Decl *D) { D->print(OS, Indent+2); }
  void printRec(Stmt *S) { S->print(OS, Indent+2); }

  void visitIntegerLiteralExpr(IntegerLiteralExpr *E) {
    OS.indent(Indent) << "(integer_literal_expr type='" << E->getType();
    OS << "' value=";
    if (E->getType().isNull() || E->getType()->is<DependentType>())
      OS << E->getText();
    else
      OS << E->getValue();
    OS << ')';
  }
  void visitFloatLiteralExpr(FloatLiteralExpr *E) {
    OS.indent(Indent) << "(float_literal_expr type='" << E->getType();
    OS << "' value=" << E->getText() << ')';
  }
  void visitDeclRefExpr(DeclRefExpr *E) {
    OS.indent(Indent) << "(declref_expr type='" << E->getType();
    OS << "' decl=" << E->getDecl()->getName() << ')';
  }
  void visitOverloadSetRefExpr(OverloadSetRefExpr *E) {
    OS.indent(Indent) << "(overloadsetref_expr type='" << E->getType();
    OS << "' decl=" << E->getDecls()[0]->getName() << " #decls="
       << E->getDecls().size() << ')';
  }
  void visitUnresolvedDeclRefExpr(UnresolvedDeclRefExpr *E) {
    OS.indent(Indent) << "(unresolved_decl_ref_expr type='" << E->getType();
    OS << "' name=" << E->getName() << ')';
  }
  void visitUnresolvedMemberExpr(UnresolvedMemberExpr *E) {
    OS.indent(Indent) << "(unresolved_member_expr type='" << E->getType();
    OS << "\' name='" << E->getName() << "')";
  }
  void visitUnresolvedScopedIdentifierExpr(UnresolvedScopedIdentifierExpr *E) {
    OS.indent(Indent) << "(unresolved_scoped_identifier_expr base='"
      << E->getBaseTypeFromScope()->getName() << "\' name='"
      << E->getName() << "')";
  }
  void visitParenExpr(ParenExpr *E) {
    OS.indent(Indent) << "(paren_expr type='" << E->getType() << "'\n";
    printRec(E->getSubExpr());
    OS << ')';
  }
  void visitTupleExpr(TupleExpr *E) {
    OS.indent(Indent) << "(tuple_expr type='" << E->getType() << '\'';
    for (unsigned i = 0, e = E->getNumElements(); i != e; ++i) {
      OS << '\n';
      if (E->getElement(i))
        printRec(E->getElement(i));
      else
        OS.indent(Indent+2) << "<<tuple element default value>>";
    }
    OS << ')';
  }
  void visitUnresolvedDotExpr(UnresolvedDotExpr *E) {
    OS.indent(Indent) << "(unresolved_dot_expr type='" << E->getType();
    OS << "\' field '" << E->getName().str() << "'";
    if (E->getBase()) {
      OS << '\n';
      printRec(E->getBase());
    }
    OS << ')';
  }
  void visitLookThroughOneofExpr(LookThroughOneofExpr *E) {
    OS.indent(Indent) << "(look_through_oneof_expr type='" << E->getType();
    OS << "\'\n";
    printRec(E->getSubExpr());
    OS << ')';
  }
  void visitTupleElementExpr(TupleElementExpr *E) {
    OS.indent(Indent) << "(tuple_element_expr type='" << E->getType();
    OS << "\' field #" << E->getFieldNumber() << "\n";
    printRec(E->getBase());
    OS << ')';
  }
  void visitTupleShuffleExpr(TupleShuffleExpr *E) {
    OS.indent(Indent) << "(tuple_shuffle type='" << E->getType();
    OS << "' Elements=[";
    for (unsigned i = 0, e = E->getElementMapping().size(); i != e; ++i) {
      if (i) OS << ", ";
      OS << E->getElementMapping()[i];
    }
    OS << "]\n";
    printRec(E->getSubExpr());
    OS << ')';
  }

  void visitLoadExpr(LoadExpr *E) {
    visit(E->getSubExpr());
  }

  void visitSequenceExpr(SequenceExpr *E) {
    OS.indent(Indent) << "(sequence_expr type='" << E->getType() << '\'';
    for (unsigned i = 0, e = E->getNumElements(); i != e; ++i) {
      OS << '\n';
      printRec(E->getElement(i));
    }
    OS << ')';
  }
  void visitFuncExpr(FuncExpr *E) {
    OS.indent(Indent) << "(func_expr type='" << E->getType() << "'\n";
    printRec(E->getBody());
    OS << ')';
  }
  void visitClosureExpr(ClosureExpr *E) {
    OS.indent(Indent) << "(closure_expr type='" << E->getType() << "'\n";
    printRec(E->getInput());
    OS << ')';
  }
  
  void visitAnonClosureArgExpr(AnonClosureArgExpr *E) {
    OS.indent(Indent) << "(anon_closure_arg_expr type='" << E->getType();
    OS << "' ArgNo=" << E->getArgNumber() << ')';
  }
  
  void visitApplyExpr(ApplyExpr *E, const char *NodeName) {
    OS.indent(Indent) << '(' << NodeName << " type='" << E->getType() << "\'\n";
    printRec(E->getFn());
    OS << '\n';
    printRec(E->getArg());
    OS << ')';
  }
  
  void visitCallExpr(CallExpr *E) {
    visitApplyExpr(E, "call_expr");
  }
  void visitUnaryExpr(UnaryExpr *E) {
    visitApplyExpr(E, "unary_expr");
  }
  void visitBinaryExpr(BinaryExpr *E) {
    visitApplyExpr(E, "binary_expr");
  }
  void visitConstructorCallExpr(ConstructorCallExpr *E) {
    visitApplyExpr(E, "constructor_call_expr");
  }
  void visitDotSyntaxCallExpr(DotSyntaxCallExpr *E) {
    visitApplyExpr(E, "dot_syntax_call_expr");
  }
  void visitDotSyntaxPlusFuncUseExpr(DotSyntaxPlusFuncUseExpr *E) {
    OS.indent(Indent) << "(dot_syntax_plus_func_use type='"
       << E->getType() << "'\n";
    printRec(E->getBaseExpr());
    OS << '\n';
    printRec(E->getPlusFuncExpr());
    OS << ')';
  }    
};

} // end anonymous namespace.


void Expr::dump() const {
  print(llvm::errs());
  llvm::errs() << '\n';
}

void Expr::print(raw_ostream &OS, unsigned Indent) const {
  PrintExpr(OS, Indent).visit(const_cast<Expr*>(this));
}