Carp/docs/Todo.md

# Todo

## Milestones
* 0.3 - Hopefully done soon, fixing the most pressing issues.
* 0.4 - A nice minimal version of the language. Should be possible to use for somewhat realistic projects.
* 1.0 - The completed version of the language with all planned features and extra nice ergonomics.

## Critical Bugs
* [0.3] Need to refactor the sorting of bindings! Hacked it for now with Obj.hs:277 "visitType (Just _) = 50"
* [0.3] When referring to nonexisting type in 'the' form, the compiler barfs.
* [0.3] Can't define globals with heap allocated types (String, structs, etc.)
* [0.3] The compiler can crash when defining invalid struct types, it should present nice errors instead.
* [0.3] Allocate enough memory in the Array.str and struct.str functions.
* [0.3] When composing interfaces the concretizer needs to run more times to make sure that all types are figured out.

## Big Language Features
* [0.4] Distinguish immutable/mutable refs?
* [0.4] Generic data types (apart from Array, which already is)
* [0.4] Doc strings.

* [1.0] Tagged unions (also known as "sum types" or "enums")
* [1.0] Lambdas (anonymous functions) that compile on Windows and don't leak memory!

## Smaller Language Features ("niceties")
* [0.3] Errors in macros should present the code location of both the macro and of the code that uses of it.
* [0.3] If main returns the value of a function returning a generic type it will fail (because there is no constraint for "Int or ()")
* [0.3] Optimization: Implement '=' for refs to numeric types, that way Array.= can aviod copying each element before comparing them.

* [0.4] Reintroduce the p-string patch but with support for embedded string literals.
* [0.4] Should be possible to read float literal without '.', eg. "3f" (because that's how they print sometimes)
* [0.4] Defining a local variable messes up unqualified lookup of function with the same name, e.g. (let [words (words &s)] ...)
* [0.4] The type error when setting a variable but missing the '&' is confusing: "Can't unify Int with &Int"
* [0.4] Good string functions

* [1.0] A way to assert compiler errors in tests
* [1.0] Rename type variables from t0, t1, t2 to a, b, c, etc.

## Macro System
* [0.3] Some lists and similar things generated by built in dynamic functions like 'cons' etc don't create proper Info for their XObjs

* [1.0] Quasiquote
* [1.0] Splicing in macros
* [1.0] Pattern matching on arguments in macros?

## Tooling
* [0.3] Project setting for turning off bound checks and similar.
* [0.3] Errors in the parser or emitter don't stop evaluation, only errors during evaluation?
* [0.3] Somehow make it possible to enter ":t foo" at the REPL (can't be done now because each atom is evaluated separately)
* [0.3] The (project-set! ...) command should accept args of various types, not just String.

* [0.4] Print a warning when changing the type of a function (can create bugs by overriding earlier declarations with the same name)
* [0.4] Hide instances of templates/generic functions when printing the environment (by default, allow it as a setting)
* [0.4] Entering the name of a symbol at the REPL prints nothing.
* [0.4] Show "call stack" when getting an error during concretization.

* [1.0] Preserve whitespace to allow saving forms back to disk
* [1.0] Refactorings at the REPL. Rename, extract function, add/remove parameter?

## Code generation
* [1.X] LLVM backend
* [?] Emit #LINE macros in the generated C code

## Ugliness
* [0.3] The 'range' function is fully generic (for all 'a') but only compiles when 'a' is numeric type. Make a check for this in the template. Or rewrite it as a normal function, that should solve it.
* [1.0] Would be nice if Info from deftypes propagated to the templates for source location of their member functions.
* [1.0] Remove unnecessary Array-functions and rewrite them in Carp?
* [1.0] "Setting" of string literals? (let [x "a"] (set! x @"b"))

## Language Design Considerations
* What's the correct type of the variable in a set!-form, i.e. (set! &x value) or (set! x value)
* How should passing primitive types (that do not care about being referenced) as ref:ed parameters be handled?
* How to handle heap allocated values? Box type with reference count?
* Fixed-size stack allocated arrays would be useful (also as members of structs)
* Macros in modules must be qualified right now, is that a good long-term solution?
* Allow use of 'the' as a wrapper when defining a variable or function, i.e. (the (Fn [Int] Int) (defn [x] x))?
* Being able to use 'the' in function parameter declarations, i.e. (defn f [(the Int x)] x) to enforce a type?