Script to install Haxe 3.0.0-RC2 along with another Haxe version. Create a symbolic link in /usr/lib/haxe which will target haxe3, but you can easily change it to target your older version (renamed /usr/lib/haxe2). Must be executed as root.

install-haxe-osx

#!/bin/bash
if [[ -z $1]]; then
  v=3.0.0
else
	v=$1
fi
echo "Downloading and installing Haxe3"
curl http://haxe.org/file/haxe-$v-osx.tar.gz -o haxe-$v-osx.tar.gz &&
tar -xzf haxe-$v-osx.tar.gz &&

# Rename your old haxe version
mv /usr/lib/haxe /usr/lib/haxe2 &&

# Create a dir for the new one
mkdir /usr/lib/haxe3 &&
cp -r haxe-$v-osx/* /usr/lib/haxe3 &&

# Create the link that will make the switch
ln -s /usr/lib/haxe3 /usr/lib/haxe &&
mv /usr/lib/haxe3/haxelib /usr/lib/haxe3/haxelib_bak &&
cp haxe-$v-osx/std/tools/haxelib/haxelib.sh /usr/lib/haxe3/haxelib &&
chmod +x /usr/lib/haxe3/haxelib &&
mkdir /usr/lib/haxe3/lib &&
chmod 777 /usr/lib/haxe3/lib &&

# Clean
rm -rf haxe-$v-osx.tar.gz haxe-$v-osx &&
echo "Haxe $v installed successfully!"

echo "Downloading and installing Neko 2"
curl http://nekovm.org/_media/neko-2.0.0-osx.tar.gz -o neko-2.0.0-osx.tar.gz &&
tar -xzf neko-2.0.0-osx.tar.gz &&
cp neko-2.0.0-osx/libneko.dylib /usr/lib &&
cp neko-2.0.0-osx/neko neko-2.0.0-osx/nekoc neko-2.0.0-osx/nekotools neko-2.0.0-osx/nekoml neko-2.0.0-osx/nekoml.std /usr/bin &&
cp neko-2.0.0-osx/*.ndll /usr/lib/neko
neko neko-2.0.0-osx/test.n
rm -rf neko-2.0.0-osx.tar.gz neko-2.0.0-osx