Regions

Mark-compact for acyclic objects

Convert ANF to relaxed ANF then to PZ. Use the relaxed ANF to find single use variables and optimize them away to generate more efficient PZ. Do some other def-use analysis too, including for parallel tasks.

Use structural matching to some degree, an instance can implement more than one interface, and may define more than an interface requires.

When supporting interfaces, maybe they can be integrated with the package system in a kind-of "does this package provide X?"

Evaluate HKTs.

Refinement types / path-aware constraints.

Use symbols like ? for maybe and | for or, like Flow Types.

Consider safe/unsafe integer operations such as overflows, division by zero etc. Allow checking for error to be done at the end of a complex calculation or by throwing an exception. + When implementing more subtyping, during an ambigious type which the value of a match expression, prefer the type (if there is one) that allows the match to "cover" the whole type, and provide that as guidance to the solver.

Add field update and conditional field update syntax.

Maybe remove parens from if-then-else conditions and other places such as match parameters.

Guards on cases

Disjunctive patterns on cases

SISAL allows "masks" (like guards or filters) on returns clauses of loops. This looks pretty powerful.

More succinct loop syntax, for simpler loops.

Maybe allow simple loop outputs to be specified in the loop "head".

Consider different syntax & and ,? for combining multiple loop inputs in lockstep or Cartesian combinations.

List, array and sequence comprehensions.

Add a scope statement that contains a block allowing shadowing of some variables, and hiding of any produced variables.

Add let expressions?

Add something to allow statements within expressions?

Probably drop { } for dictionary constants in favor of [ ] with a ⇒ to separate keys from values. + Add more logical operators to the langauge, maybe xor and implication, probably via keywords or functions rather than symbols.

Predicate expressions as a syntax sugar for applicative.

Language "levels"

Various ideas around resources and higher-order code:

Read about Facebook reason wrt naming things and syntax.

Use command line parsing as example code for language & library.