This package contains the "unambiguous choice" operator unamb, which wraps thread racing up in a purely functional, semantically simple wrapper. Given any two arguments u and v that agree unless bottom, the value of unamb u v is the more terminating of u and v. Operationally, the value of unamb u v becomes available when the earlier of u and v does. The agreement precondition ensures unamb's referential transparency.

unamb and a sample use appeared in the paper Push-pull functional reactive programming. I moved it to its own package in order to encourage experimentation.

Note that unamb correctly implements the least-upper-bound operation (on information content), also known as "lub" or "(⊔)", but only for flat types (in which values are completely undefined or completely defined). I suggest using the lub package instead of unamb. (Also on GitHub.)