Perl Also see TODO.
"function signatures", or rather runtime function argument type checks, using type predicate functions: does Method::Signatures need to be modified to support this? (Or should Function::Parameters be used instead?)
reimplement parts in C (Pair, perhaps Promise?) to save some space and CPU (but then, that prevents serialization [unless more work is done]; also, to really optimize, want a custom/fake SV type that includes the pair fields directly?)
read-only enforcing versions of the functional data structures (or, read-only by default, then togglable [or just offering unsafe usually-forbidden] mutators); including, especially, FP::Struct as potential building block of such data structures
write sequences API declaration, to code alternative implementations against for optimization purposes (runtime coalescence of chained operations (something like ->map($f1)->map($f2)->filter($f3)->fold($f4,$x) = ->map_filter_fold(compose($f1,$f2),$f3,$f4,$x)) (or would deforestation be feasible? Or just compile time optimization of the same as above?)
add set API, make FP::HashSet and OO based port.
a variant of Scalar::Util's weaken that takes a value to be put into the spot that held a reference when it is deleted, so that the user can see something more useful like an object that carries a message "weakened by stream_ref" (perhaps including caller location) or some such instead of undef
Or, fix the perl interpreter, after all (lexical variable life time analysis.) Could this be done as a module working on the byte code?
Byte code optimizer that automatically turns function calls in tail position into gotos, if some 'TCO' pragma is in effect
Provide a 'recursive let' form that includes weakening or application of the fix point combinator
change FP::Struct into a Moose extension? Is Moose ok to have as a hard dependency? (Because why are there all these Moose alternatives like Moo?)
Are MooseX::Locked, MooseX::MultiMethods good?
What about the nice-and-simple predicate approach? Extend that to make multimethod dispatch still fast? Would that then (really?) be the same as Moose::Util::TypeConstraints?
add functional vector implementation with good computational complexity (see paper from which Clojure implemented theirs), perhaps base FP::PureArray on it, implement functional hashmap on it, implement set with it. (There are implementations on JavaScript too, already. Are there any in C?)
currying, pattern matching, multimethods, ...: see if existing modules can be used. Experiment, embrace, extend...
serialisation of closures: should we provide helpers to create closures that can be serialised on older Perl releases, or should we depend on newest Perl and a serializer that can handle normal closures?
improve website layout
when linking to an anchor (like todo.xhtml#Names) is there a way (without javascript) to make the linked-to item (section header) appear high-lighted or something (if the end of the page isn't reached, then it's visually clear which item is meant, but items towards the end of the page don't have that luxury)
Add AUTOLOAD to FP::List to auto-generate lisp style c[ad]*r accessors? Benchmark the overhead of adding a DESTROY method, though!
Not such a good idea since (a) is someone really using them much?, (b) complexity. (See the c_r method already implemented first.)