There is now an OS X installer of this "pre 7.10.2 - we'll just call it alpha 3" Platform, again, built with head of GHC 7.10 branch this morning:

Haskell Platform 7.10.1.20150601 alpha 3 64bit.pkg

SHA-256: 65adae24b0a75e23c77632e7375198b4f3158e49984e3a1afec452d7ae5832ce

Watch out... it weighs 230MiB!