Haskell will take months of brain twisting before you really understand what is going on and can do anything productive. ReasonML, you could be up and running within a week. (Timescales are just a random guess, but you get the idea..)
Plus ReasonML isn't strictly functional. You can have side effects and mutation if you need. Obviously the purists may view this as a negative, but being able to eg. just get a random number without going through a ton of hoops can make things a bit less frustrating - especially if you are unfamiliar with functional.
Once you have a good grasp of functional through ReasonML, Haskell will feel a lot less daunting.
Plus ReasonML isn't strictly functional. You can have side effects and mutation if you need. Obviously the purists may view this as a negative, but being able to eg. just get a random number without going through a ton of hoops can make things a bit less frustrating - especially if you are unfamiliar with functional.
Once you have a good grasp of functional through ReasonML, Haskell will feel a lot less daunting.