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+//===- AST.cpp - Helper for printing out the Toy AST ----------------------===//
+//
+// Copyright 2019 The MLIR Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// =============================================================================
+//
+// This file implements the AST dump for the Toy language.
+//
+//===----------------------------------------------------------------------===//
+
+#include "toy/AST.h"
+
+#include "llvm/ADT/Twine.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace toy;
+
+namespace {
+
+// RAII helper to manage increasing/decreasing the indentation as we traverse
+// the AST
+struct Indent {
+  Indent(int &level) : level(level) { ++level; }
+  ~Indent() { --level; }
+  int &level;
+};
+
+/// Helper class that implement the AST tree traversal and print the nodes along
+/// the way. The only data member is the current indentation level.
+class ASTDumper {
+public:
+  void dump(ModuleAST *Node);
+
+private:
+  void dump(VarType &type);
+  void dump(VarDeclExprAST *varDecl);
+  void dump(ExprAST *expr);
+  void dump(ExprASTList *exprList);
+  void dump(NumberExprAST *num);
+  void dump(LiteralExprAST *Node);
+  void dump(VariableExprAST *Node);
+  void dump(ReturnExprAST *Node);
+  void dump(BinaryExprAST *Node);
+  void dump(CallExprAST *Node);
+  void dump(PrintExprAST *Node);
+  void dump(PrototypeAST *Node);
+  void dump(FunctionAST *Node);
+
+  // Actually print spaces matching the current indentation level
+  void indent() {
+    for (int i = 0; i < curIndent; i++)
+      llvm::errs() << "  ";
+  }
+  int curIndent = 0;
+};
+
+} // namespace
+
+/// Return a formatted string for the location of any node
+template <typename T> static std::string loc(T *Node) {
+  const auto &loc = Node->loc();
+  return (llvm::Twine("@") + *loc.file + ":" + llvm::Twine(loc.line) + ":" +
+          llvm::Twine(loc.col))
+      .str();
+}
+
+// Helper Macro to bump the indentation level and print the leading spaces for
+// the current indentations
+#define INDENT()                                                               \
+  Indent level_(curIndent);                                                    \
+  indent();
+
+/// Dispatch to a generic expressions to the appropriate subclass using RTTI
+void ASTDumper::dump(ExprAST *expr) {
+#define dispatch(CLASS)                                                        \
+  if (CLASS *node = llvm::dyn_cast<CLASS>(expr))                               \
+    return dump(node);
+  dispatch(VarDeclExprAST);
+  dispatch(LiteralExprAST);
+  dispatch(NumberExprAST);
+  dispatch(VariableExprAST);
+  dispatch(ReturnExprAST);
+  dispatch(BinaryExprAST);
+  dispatch(CallExprAST);
+  dispatch(PrintExprAST);
+  // No match, fallback to a generic message
+  INDENT();
+  llvm::errs() << "<unknown Expr, kind " << expr->getKind() << ">\n";
+}
+
+/// A variable declaration is printing the variable name, the type, and then
+/// recurse in the initializer value.
+void ASTDumper::dump(VarDeclExprAST *varDecl) {
+  INDENT();
+  llvm::errs() << "VarDecl " << varDecl->getName();
+  dump(varDecl->getType());
+  llvm::errs() << " " << loc(varDecl) << "\n";
+  dump(varDecl->getInitVal());
+}
+
+/// A "block", or a list of expression
+void ASTDumper::dump(ExprASTList *exprList) {
+  INDENT();
+  llvm::errs() << "Block {\n";
+  for (auto &expr : *exprList)
+    dump(expr.get());
+  indent();
+  llvm::errs() << "} // Block\n";
+}
+
+/// A literal number, just print the value.
+void ASTDumper::dump(NumberExprAST *num) {
+  INDENT();
+  llvm::errs() << num->getValue() << " " << loc(num) << "\n";
+}
+
+/// Helper to print recurisvely a literal. This handles nested array like:
+///    [ [ 1, 2 ], [ 3, 4 ] ]
+/// We print out such array with the dimensions spelled out at every level:
+///    <2,2>[<2>[ 1, 2 ], <2>[ 3, 4 ] ]
+void printLitHelper(ExprAST *lit_or_num) {
+  // Inside a literal expression we can have either a number or another literal
+  if (auto num = llvm::dyn_cast<NumberExprAST>(lit_or_num)) {
+    llvm::errs() << num->getValue();
+    return;
+  }
+  auto *literal = llvm::cast<LiteralExprAST>(lit_or_num);
+
+  // Print the dimension for this literal first
+  llvm::errs() << "<";
+  {
+    const char *sep = "";
+    for (auto dim : literal->getDims()) {
+      llvm::errs() << sep << dim;
+      sep = ", ";
+    }
+  }
+  llvm::errs() << ">";
+
+  // Now print the content, recursing on every element of the list
+  llvm::errs() << "[ ";
+  const char *sep = "";
+  for (auto &elt : literal->getValues()) {
+    llvm::errs() << sep;
+    printLitHelper(elt.get());
+    sep = ", ";
+  }
+  llvm::errs() << "]";
+}
+
+/// Print a literal, see the recursive helper above for the implementation.
+void ASTDumper::dump(LiteralExprAST *Node) {
+  INDENT();
+  llvm::errs() << "Literal: ";
+  printLitHelper(Node);
+  llvm::errs() << " " << loc(Node) << "\n";
+}
+
+/// Print a variable reference (just a name).
+void ASTDumper::dump(VariableExprAST *Node) {
+  INDENT();
+  llvm::errs() << "var: " << Node->getName() << " " << loc(Node) << "\n";
+}
+
+/// Return statement print the return and its (optional) argument.
+void ASTDumper::dump(ReturnExprAST *Node) {
+  INDENT();
+  llvm::errs() << "Return\n";
+  if (Node->getExpr().hasValue())
+    return dump(*Node->getExpr());
+  {
+    INDENT();
+    llvm::errs() << "(void)\n";
+  }
+}
+
+/// Print a binary operation, first the operator, then recurse into LHS and RHS.
+void ASTDumper::dump(BinaryExprAST *Node) {
+  INDENT();
+  llvm::errs() << "BinOp: " << Node->getOp() << " " << loc(Node) << "\n";
+  dump(Node->getLHS());
+  dump(Node->getRHS());
+}
+
+/// Print a call expression, first the callee name and the list of args by
+/// recursing into each individual argument.
+void ASTDumper::dump(CallExprAST *Node) {
+  INDENT();
+  llvm::errs() << "Call '" << Node->getCallee() << "' [ " << loc(Node) << "\n";
+  for (auto &arg : Node->getArgs())
+    dump(arg.get());
+  indent();
+  llvm::errs() << "]\n";
+}
+
+/// Print a builtin print call, first the builtin name and then the argument.
+void ASTDumper::dump(PrintExprAST *Node) {
+  INDENT();
+  llvm::errs() << "Print [ " << loc(Node) << "\n";
+  dump(Node->getArg());
+  indent();
+  llvm::errs() << "]\n";
+}
+
+/// Print type: only the shape is printed in between '<' and '>'
+void ASTDumper::dump(VarType &type) {
+  llvm::errs() << "<";
+  const char *sep = "";
+  for (auto shape : type.shape) {
+    llvm::errs() << sep << shape;
+    sep = ", ";
+  }
+  llvm::errs() << ">";
+}
+
+/// Print a function prototype, first the function name, and then the list of
+/// parameters names.
+void ASTDumper::dump(PrototypeAST *Node) {
+  INDENT();
+  llvm::errs() << "Proto '" << Node->getName() << "' " << loc(Node) << "'\n";
+  indent();
+  llvm::errs() << "Params: [";
+  const char *sep = "";
+  for (auto &arg : Node->getArgs()) {
+    llvm::errs() << sep << arg->getName();
+    sep = ", ";
+  }
+  llvm::errs() << "]\n";
+}
+
+/// Print a function, first the prototype and then the body.
+void ASTDumper::dump(FunctionAST *Node) {
+  INDENT();
+  llvm::errs() << "Function \n";
+  dump(Node->getProto());
+  dump(Node->getBody());
+}
+
+/// Print a module, actually loop over the functions and print them in sequence.
+void ASTDumper::dump(ModuleAST *Node) {
+  INDENT();
+  llvm::errs() << "Module:\n";
+  for (auto &F : *Node)
+    dump(&F);
+}
+
+namespace toy {
+
+// Public API
+void dump(ModuleAST &module) { ASTDumper().dump(&module); }
+
+} // namespace toy