diff --git a/bootstrap/emit.cc b/bootstrap/emit.cc
index e478853..9589e3b 100644
--- a/bootstrap/emit.cc
+++ b/bootstrap/emit.cc
@@ -1,38 +1,163 @@
 #include <emit.hh>
-#include <iostream>
+#include <vector>
 
 namespace xlang {
 
-EmitListener::EmitListener(std::string_view outputfile) : output{outputfile} {}
+class EmitFunctionVisitor : public xlangBaseVisitor {};
 
-void EmitListener::enterFile(xlangParser::FileContext *ctx) {
-  output << "data $printformat = { b \"%ld\\n\", b 0 }" << std::endl;
-  (void)ctx;
+EmitVisitor::EmitVisitor(std::string_view outputfile) : output{outputfile} {}
+
+std::any EmitVisitor::visitFile(xlangParser::FileContext *ctx) {
+  output << "data $printformat = { b \"%d\\n\", b 0 }" << std::endl;
+  visitChildren(ctx);
+  return {};
 }
 
-void EmitListener::enterFunction(xlangParser::FunctionContext *ctx) {
+std::any EmitVisitor::visitFunction(xlangParser::FunctionContext *ctx) {
   output << std::endl
          << "export function w $" << ctx->Identifier()->getSymbol()->getText()
-         << "()" << std::endl
-         << "{" << std::endl
-         << "@start" << std::endl;
+         << "(";
+  if (auto arg_list = ctx->argumentList()) {
+    for (const auto arg : arg_list->Identifier()) {
+      output << "w %_" << arg->getSymbol()->getText() << ", ";
+    }
+  }
+  output << ")" << std::endl << "{" << std::endl << "@start" << std::endl;
+  blockcount = 0;
+  visitChildren(ctx);
+  output << "  ret 0" << std::endl;
+  output << "}" << std::endl;
+  return {};
 }
 
-void EmitListener::exitFunction(xlangParser::FunctionContext *ctx) {
-  output << "  ret 0" << std::endl << "}" << std::endl;
-  (void)ctx;
+std::any EmitVisitor::visitBlock(xlangParser::BlockContext *ctx) {
+  output << "@block" << blockcount++ << std::endl;
+  visitChildren(ctx);
+  return {};
 }
 
-void EmitListener::exitStatement(xlangParser::StatementContext *ctx) {
+std::any EmitVisitor::visitStatement(xlangParser::StatementContext *ctx) {
+  if (auto identifier = ctx->Identifier()) {
+    tmpcount = 0;
+    visitChildren(ctx);
+    output << "  %_" << identifier->getSymbol()->getText() << " = w copy %t"
+           << tmpcount - 1 << std::endl;
+    return {};
+  }
+  if (ctx->If()) {
+    int block = blockcount;
+    output << "@ifexpr" << block << std::endl;
+    tmpcount = 0;
+    visitExpr(ctx->expr());
+    output << "  jnz %t" << tmpcount - 1 << ", @block" << block << ", @ifelse"
+           << block << std::endl;
+    visitBlock(ctx->block(0));
+    output << "@ifelse" << block << std::endl;
+    if (ctx->Else()) {
+      visitBlock(ctx->block(1));
+    }
+    output << "@ifend" << block << std::endl;
+    return {};
+  }
+  if (ctx->While()) {
+    int block = blockcount;
+    output << "@whileexpr" << block << std::endl;
+    tmpcount = 0;
+    visitExpr(ctx->expr());
+    output << "  jnz %t" << tmpcount - 1 << ", @block" << block << ", @whileend"
+           << block << std::endl;
+    visitBlock(ctx->block(0));
+    output << "  jmp @whileexpr" << block << std::endl;
+    output << "@whileend" << block << std::endl;
+    return {};
+  }
+  if (ctx->Return()) {
+    tmpcount = 0;
+    visitChildren(ctx);
+    output << "  ret %t" << tmpcount - 1 << std::endl;
+    output << "@dead" << blockcount++ << std::endl;
+    return {};
+  }
   if (ctx->Print()) {
-    output << "  call $printf(l $printformat, ..., w %v)" << std::endl;
+    tmpcount = 0;
+    visitChildren(ctx);
+    output << "  call $printf(l $printformat, ..., w %t" << tmpcount - 1 << ")"
+           << std::endl;
+    return {};
   }
+  // unreachable
+  return {};
 }
 
-void EmitListener::exitFactor(xlangParser::FactorContext *ctx) {
-  if (auto integer = ctx->Integer()) {
-    output << "  %v = w copy " << integer->getSymbol()->getText() << std::endl;
+#define OPERATOR(Operator, visitLeft, left, visitRight, right, ssa_op)   \
+  if (ctx->Operator()) {                                                 \
+    visitLeft(ctx->left);                                                \
+    int l = tmpcount - 1;                                                \
+    visitRight(ctx->right);                                              \
+    output << "  %t" << tmpcount << " = w " ssa_op " %t" << l << ", %t" \
+           << tmpcount - 1 << std::endl;                                 \
+    tmpcount++;                                                          \
+    return {};                                                           \
   }
+
+std::any EmitVisitor::visitExpr(xlangParser::ExprContext *ctx) {
+  OPERATOR(Less, visitSum, sum(0), visitSum, sum(1), "csltw");
+  OPERATOR(LessEqual, visitSum, sum(0), visitSum, sum(1), "cslew");
+  OPERATOR(Greater, visitSum, sum(0), visitSum, sum(1), "csgtw");
+  OPERATOR(GreaterEqual, visitSum, sum(0), visitSum, sum(1), "csgew");
+  OPERATOR(Equal, visitSum, sum(0), visitSum, sum(1), "ceqw");
+  OPERATOR(NotEqual, visitSum, sum(0), visitSum, sum(1), "cnew");
+  visitSum(ctx->sum(0));
+  return {};
+}
+
+std::any EmitVisitor::visitSum(xlangParser::SumContext *ctx) {
+  OPERATOR(Plus, visitSum, sum(), visitTerm, term(), "add");
+  OPERATOR(Minus, visitSum, sum(), visitTerm, term(), "sub");
+  visitTerm(ctx->term());
+  return {};
+}
+
+std::any EmitVisitor::visitTerm(xlangParser::TermContext *ctx) {
+  OPERATOR(Mul, visitTerm, term(), visitFactor, factor(), "mul");
+  OPERATOR(Div, visitTerm, term(), visitFactor, factor(), "div");
+  visitFactor(ctx->factor());
+  return {};
+}
+
+std::any EmitVisitor::visitFactor(xlangParser::FactorContext *ctx) {
+  if (auto integer = ctx->Integer()) {
+    output << "  %t" << tmpcount++ << " = w copy "
+           << integer->getSymbol()->getText() << std::endl;
+    return {};
+  }
+  if (auto identifier = ctx->Identifier()) {
+    if (ctx->LeftParen()) {
+      std::vector<int> args;
+      if (auto expr_list = ctx->exprList()) {
+        for (auto expr : expr_list->expr()) {
+          visitExpr(expr);
+          args.push_back(tmpcount - 1);
+        }
+      }
+      output << "  %t" << tmpcount++ << " = w call $"
+             << identifier->getSymbol()->getText() << "(";
+      for (auto arg : args) {
+        output << "w %t" << arg << ", ";
+      }
+      output << ")" << std::endl;
+    } else {
+      output << "  %t" << tmpcount++ << " = w copy %_"
+             << identifier->getSymbol()->getText() << std::endl;
+    }
+    return {};
+  }
+  if (auto sum = ctx->sum()) {
+    visitSum(sum);
+    return {};
+  }
+  // unreachable
+  return {};
 }
 
 }  // namespace xlang
diff --git a/bootstrap/emit.hh b/bootstrap/emit.hh
index 405f63b..695171a 100644
--- a/bootstrap/emit.hh
+++ b/bootstrap/emit.hh
@@ -2,21 +2,26 @@
 
 #include <fstream>
 #include <string_view>
-#include <xlangBaseListener.h>
+#include <xlangBaseVisitor.h>
 
 namespace xlang {
 
-class EmitListener : public xlangBaseListener {
+class EmitVisitor : public xlangBaseVisitor {
   std::ofstream output;
+  int blockcount;
+  int tmpcount;
 
  public:
-  EmitListener(std::string_view outputfile);
+  EmitVisitor(std::string_view outputfile);
 
-  void enterFile(xlangParser::FileContext *ctx) override;
-  void enterFunction(xlangParser::FunctionContext *ctx) override;
-  void exitFunction(xlangParser::FunctionContext *ctx) override;
-  void exitStatement(xlangParser::StatementContext *ctx) override;
-  void exitFactor(xlangParser::FactorContext *ctx) override;
+  std::any visitFile(xlangParser::FileContext *ctx) override;
+  std::any visitFunction(xlangParser::FunctionContext *ctx) override;
+  std::any visitBlock(xlangParser::BlockContext *ctx) override;
+  std::any visitStatement(xlangParser::StatementContext *ctx) override;
+  std::any visitExpr(xlangParser::ExprContext *ctx) override;
+  std::any visitSum(xlangParser::SumContext *ctx) override;
+  std::any visitTerm(xlangParser::TermContext *ctx) override;
+  std::any visitFactor(xlangParser::FactorContext *ctx) override;
 };
 
 }  // namespace xlang
diff --git a/bootstrap/main.cc b/bootstrap/main.cc
index 4c4c6c3..888b0b7 100644
--- a/bootstrap/main.cc
+++ b/bootstrap/main.cc
@@ -43,7 +43,7 @@ int main(int argc, char **argv) {
   xlang::xlangParser parser{&tokens};
   auto *tree = parser.file();
 
-  xlang::EmitListener emit{outputfile};
-  antlr4::tree::ParseTreeWalker::DEFAULT.walk(&emit, tree);
+  xlang::EmitVisitor emit{outputfile};
+  emit.visitFile(tree);
   return 0;
 }
diff --git a/bootstrap/xlang.g4 b/bootstrap/xlang.g4
index 0c8c36d..b16bbbb 100644
--- a/bootstrap/xlang.g4
+++ b/bootstrap/xlang.g4
@@ -11,13 +11,19 @@ statement : Identifier Assign expr Semicolon
           | Print expr Semicolon
           | expr Semicolon
           ;
-expr  : sum ((Less|LessEqual|Greater|GreaterEqual|Equal|NotEqual) sum)*;
-sum : term ((Plus|Minus) term)*;
-term  : factor ((Mul|Div) factor)*;
+expr  : sum ((Less|LessEqual|Greater|GreaterEqual|Equal|NotEqual) sum)
+      | sum
+      ;
+sum : sum ((Plus|Minus) term)
+    | term
+    ;
+term  : term ((Mul|Div) factor)
+      | factor
+      ;
 factor  : Integer
         | Identifier
         | Identifier LeftParen exprList? RightParen
-        | LeftParen expr RightParen
+        | LeftParen sum RightParen
         ;
 exprList  : expr (Comma expr)*;
 
@@ -45,7 +51,7 @@ Div : '/';
 Comma : ',';
 Semicolon : ';';
 
-Identifier  : [a-zA-Z][a-zA-Z0-9]*;
+Identifier  : [_a-zA-Z][_a-zA-Z0-9]*;
 Integer : [0-9]+;
 
 Comment : '//' ~[\n]* '\n' -> skip;
diff --git a/test/fib.x b/test/fib.x
index f6133fb..fb2690b 100644
--- a/test/fib.x
+++ b/test/fib.x
@@ -1,10 +1,20 @@
 main() {
-  // print 5th fibonacci number
-  print fib(5);
-  return 0;
+  i = 0;
+  while i < 10 {
+    print fib_rec(i);
+    print fib_iter(i);
+    i = i + 1;
+  }
 }
 
-fib(n) {
+fib_rec(n) {
+  if n < 2 {
+    return 1;
+  }
+  return fib_rec(n - 1) + fib_rec(n - 2);
+}
+
+fib_iter(n) {
   x0 = 1;
   x1 = 1;
   i = 0;