diff --git a/src/ast.c b/src/ast.c
new file mode 100644
index 00000000..ce38f442
--- /dev/null
+++ b/src/ast.c
@@ -0,0 +1,10 @@
+#include "ast.h"
+#include <assert.h>
+
+const char* ast_info(enum AstTag tag) {
+  static const char* const tag_info[] = {
+    "IDENTIFIER",
+  };
+  assert(sizeof(tag_info)/sizeof(char*) == AST_TAG_ENUM_END);
+  return tag_info[tag];
+}
diff --git a/src/ast.h b/src/ast.h
index 424a2620..454617ac 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -2,7 +2,10 @@
 #define KMC_C90_COMPILER_AST_H
 
 enum AstTag {
-  AST_IDENTIFIER
+  AST_IDENTIFIER,
+  AST_TAG_ENUM_END
 };
 
+const char* ast_info(enum AstTag tag);
+
 #endif  /* KMC_C90_COMPILER_AST_H */
diff --git a/src/sexpr.c b/src/sexpr.c
index 7a695cba..e89020a9 100644
--- a/src/sexpr.c
+++ b/src/sexpr.c
@@ -66,3 +66,42 @@ enum AstTag sexpr_get_ast(SexprRef sexpr) {
   assert(sexpr_is_ast(sexpr));
   return sexpr->data.ast;
 }
+
+static void indent(FILE* stream, int depth) {
+  int i = 0;
+  for (; i < depth; ++i) {
+    fprintf(stream, " ");
+  }
+}
+static void sexpr_print_impl(FILE* stream, SexprRef sexpr, int depth) {
+  if (sexpr_is_pair(sexpr)) {
+    if (sexpr_is_atom(car(sexpr))) {
+      sexpr_print_impl(stream, car(sexpr), depth);
+    } else {
+      fprintf(stream, "(");
+      sexpr_print_impl(stream, car(sexpr), depth + 1);
+      fprintf(stream, ")");
+    }
+    if (sexpr_is_atom(cdr(sexpr))) {
+      fprintf(stream, " . ");
+      sexpr_print_impl(stream, cdr(sexpr), depth + 3);
+    } else if (sexpr_is_pair(cdr(sexpr))) {
+      fprintf(stream, "\n");
+      indent(stream, depth);
+      sexpr_print_impl(stream, cdr(sexpr), depth);
+    }
+  } else if (sexpr_is_symbol(sexpr)) {
+    fprintf(stream, "%s", string_data(sexpr_get_symbol(sexpr)));
+  } else if (sexpr_is_ast(sexpr)) {
+    fprintf(stream, "%s", ast_info(sexpr_get_ast(sexpr)));
+  }
+}
+void sexpr_print(FILE* stream, SexprRef sexpr) {
+  if (sexpr_is_atom(sexpr)) {
+    sexpr_print_impl(stream, sexpr, 0);
+  } else {
+    fprintf(stream, "(");
+    sexpr_print_impl(stream, sexpr, 1);
+    fprintf(stream, ")\n");
+  }
+}
diff --git a/src/sexpr.h b/src/sexpr.h
index 0261cbf4..b9d23ed4 100644
--- a/src/sexpr.h
+++ b/src/sexpr.h
@@ -1,6 +1,7 @@
 #ifndef KMC_C90_COMPILER_SEXPR_H
 #define KMC_C90_COMPILER_SEXPR_H
 
+#include <stdio.h>
 #include "ast.h"
 #include "stdstring.h"
 #include "utility.h"
@@ -43,4 +44,6 @@ StringRef sexpr_get_symbol(SexprRef sexpr);
 SexprRef sexpr_make_ast(enum AstTag ast);
 enum AstTag sexpr_get_ast(SexprRef sexpr);
 
+void sexpr_print(FILE* stream, SexprRef sexpr);
+
 #endif  /* KMC_C90_COMPILER_SEXPR_H */
diff --git a/tests/lexer_test/Makefile b/tests/lexer_test/Makefile
index f570ae61..b64fc1d8 100644
--- a/tests/lexer_test/Makefile
+++ b/tests/lexer_test/Makefile
@@ -9,7 +9,7 @@ include $(TOP_DIR)/Makefile.common
 include $(GTEST_DIR)/Makefile.common
 include $(TESTS_DIR)/Makefile.common
 
-LEX_SRCS := lex.yy.c utility.c parser.tab.c allocator.c memory_pool.c stdstring.c sexpr.c sexpr_pool.c
+LEX_SRCS := lex.yy.c utility.c parser.tab.c allocator.c memory_pool.c stdstring.c sexpr.c sexpr_pool.c ast.c
 LEX_OBJS := $(LEX_SRCS:%.c=$(SRC_DIR)/%.o)
 TARGET := lexer_test.out