Fix build error

BuildMakefile

@@ -0,0 +1,16 @@
+fmt:
+	find . -iname '*.h' -o -iname '*.cpp' -o -iname '*.hpp' -o -iname '*.hh' | xargs clang-format -i
+
+check:
+	xmake check clang.tidy --configfile=.clang-tidy
+
+fix:
+	xmake check clang.tidy --configfile=.clang-tidy --fix
+
+build:
+	xmake f -m debug && xmake build -w
+
+release:
+	xmake f -m release && xmake build -w
+
+.PHONY: fmt check fix build release

README

@@ -0,0 +1,55 @@
+*  Swallow
+*  A minimalist functional programming language
+*  Copyright (c) 2023 Muqiu Han
+*  
+*  This project is built using xmake: https://xmake.io/
+*  
+*  FAQ: https://github.com/muqiuhan/Swallow/blob/main/FAQ
+*  Issues: https://github.com/muqiuhan/Swallow/issues
+*  Contribution: https://github.com/muqiuhan/Swallow/pulls
+
+
+To build and run with xmake:
+
+    setup: Install the xmake, flex and bison
+    To build:   xmake build
+    To run:     xmake run
+    To install: xmake install
+
+
+Features
+----------
+o- Typechecking
+o- Pattern match
+o- Garbage Collection
+o- Polymorphism
+
+LICENSE
+----------
+Copyright (c) 2023 Muqiu Han
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright notice,
+      this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above copyright notice,
+      this list of conditions and the following disclaimer in the documentation
+      and/or other materials provided with the distribution.
+    * Neither the name of Terifo nor the names of its contributors
+      may be used to endorse or promote products derived from this software
+      without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.