schala/TODO.md

#Typechecking Notes

(cf. cardelli paper)

Given a length function def:
````
fn length(x) {
 if x.is_null {
   0
  } else {
   succ(length(x.tail))
  }
}
````
Constraints:
.null: List a -> bool
.tail: List a -> List a
0: Nat
succ: Nat -> Nat




# TODO Items

-make the REPL more advanced!

-Plan of attack:
  -write a visitor pattern for AST
  -convert AST type to including SourceMap'd wrappers (w/ .into())
    -at the same time, amke sure the visitor pattern "skips over" the SourceMap'd stuff
    so it can just care about AST structure

- AST : maybe replace the Expression type with "Ascription(TypeName, Box<Expression>) nodes??
- parser: add a "debug" field to the Parser struct for all debug-related things

-scala-style html"dfasfsadf${}" string interpolations!

-fuzz test schala

-look into Inkwell for LLVM


*A neat idea for pattern matching optimization would be if you could match on one of several things in a list
ex:
if x {
 is (comp, LHSPat, RHSPat) if comp in ["==, "<"] -> ...
}


- https://nshipster.com/never/
-https://cranelift.readthedocs.io/en/latest/?badge=latest<Paste>

-consult http://gluon-lang.org/book/embedding-api.html

- if/match playground

simple if
`if x == 1.0 { "a" } else { "b" }`

one comparison multiple targets:
`if x == { 1.0 -> "a", 2.0 -> "b", else -> "c" }`

different comparison operators/ method calls:
`if x { == 1.0 -> "a", eq NaN -> "n", .hella() -> "h", else -> "z" }`

pattern matching/introducing bindings:
`if alice { .age < 18 -> "18", is Person("Alice", age) -> "${age}", else -> "none" }`

pattern matching w/ if-let:
`if person is Person("Alice", age) { "${age}" } else { "nope" }`

-https://soc.github.io/languages/unified-condition-syntax syntax:

`if <cond-expr>" then <then-expr> else <else-expr>`
`if <half-expr> \n <rest-expr1> then <result1-expr> \n <rest-expr2> then <result-expr2> else <result3-expr>`
-and rest-exprs (or "targets") can have 'is' for pattern-matching, actually so can a full cond-expr

UNIFIED IF EXPRESSIONS FINAL WORK:

basic syntax:

`if_expr := if discriminator '{' (guard_expr)* '}'`
`guard_expr := pattern 'then' block_or_expr'`
`pattern := rhs | is_pattern`
`is_pattern := 'is' ???`
`rhs := expression | ???`


if the only two guard patterns are true and false, then the abbreviated syntax:
`'if' discriminator 'then' block_or_expr 'else' block_or_expr`
can replace `'if' discriminator '{' 'true' 'then' block_or_expr; 'false' 'then' block_or_expr '}'`




- Next priorities: - get ADTs working, get matches working

- inclusive/exclusive range syntax like .. vs ..=

- sketch of an idea for the REPL:
        -each compiler pass should be a (procedural?) macro like
        compiler_pass!("parse", dataproducts: ["ast", "parse_tree"], {
         match parsing::parse(INPUT) {
           Ok(
                PASS.add_artifact(
        }

-should have an Idris-like `cast To From` function

- REPL:
  - want to be able to do things like `:doc Identifier`, and have the language load up these definitions to the REPL


* change 'trait' to 'interface'
  -think about idris-related ideas of multiple implementations of a type for an interface (+ vs * impl for monoids, for preorder/inorder/postorder for Foldable)

* Share state between programming languages

* idea for Schala - scoped types - be able to define a quick enum type scoped to a function ro something, that only is meant to be used as a quick bespoke interface between two other things

* another idea, allow:
type enum {
  type enum MySubVariant {
    SubVariant1, SubVariant2, etc.
    }
 Variant1(MySubVariant),
 Variant2(...),
 }



* idea for Schala: both currying *and* default arguments!
        ex. fn a(b: Int, c:Int, d:Int = 1) -> Int
            a(1,2) : Int
            a(1,2,d=2): Int
            a(_,1,3) : Int -> Int
            a(1,2, c=_): Int -> Int
            a(_,_,_) : Int -> Int -> Int -> Int





*Compiler passes architecture

-ProgrammingLanguageInterface defines a evaluate_in_repl() and evaluate_no_repl() functions
-these take in a vec of CompilerPasses

struct CompilerPass {
        name: String,
        run: fn(PrevPass) -> NextPass
}

-change "Type...." names in parser.rs to "Anno..." for non-collision with names in typechecking.rs

-get rid of code pertaining to compilation specifically, have a more generation notion of "execution type"