Strategy to map processes to processors optimally. Some particular research issues, like parallelism and efficient lazy evaluation, are the key to the success of the whole field. The existing processors are close to the physical limits of speed, any significant increases in speed performance are doubtful in the near future, one possible solution is to apply massive parallelism. This has to be supported by not only hardware but also software. It is very difficult, if not impossible, for imperative PLs to support parallism, and this gives FPLs a great role in the future PL field, when the importance of parallism is recognized, because FPLs support parallism.
Lazy evaluation is very powerful and expressive in FPLs, but it is also very slow.
Hence, the efficient lazy evaluation is crucial to the performance of FPLs besides parallelism. The formal semantic definition of Haskell is quite elegant and minimal. Try to give examples or counter-examples. Again, try to give examples. The size of a language's formal semantic definition is not directly related to the size of the language, because if a PL defines more structures, its size will be bigger.