schala/TODO.md

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# Immediate TODOs / General Code Cleanup
## Symbols
* the symbol table should probably *only* be for global definitions (maybe rename it to reflect this?)
* dealing with variable lookup w/in functions/closures should probably happen in AST -> ReducedAST
* b/c that's where we go from a string name to a canonical ID (for e.g. 2nd param in 3rd enclosing scope)
* Old notes on a plan of attack:
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1. modify visitor so it can handle scopes
-this is needed both to handle import scope correctly
-and also to support making FQSNs aware of function parameters
2. Once FQSNs are aware of function parameters, most of the Rc<String> things in eval.rs can go away
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## Parser
* I think I can restructure the parser to get rid of most instances of expect!, at least at the beginning of a rule
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## Typechecking
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* make a type to represent types rather than relying on string comparisons
* look at https://rickyhan.com/jekyll/update/2018/05/26/hindley-milner-tutorial-rust.html
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## General code cleanup
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* standardize on an error type that isn't String
* implement a visitor pattern for the use of scope_resolver
* maybe implement this twice: 1) the value-returning, no-default one in the haoyi blogpost,
* look at
* https://gitlab.haskell.org/ghc/ghc/wikis/pattern-synonyms
* the non-value-returning, default one like in rustc (cf. https://github.com/rust-unofficial/patterns/blob/master/patterns/visitor.md)
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# Longer-term Ideas
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## Language Syntax
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* the `type` declaration should have some kind of GADT-like syntax
* use `let` sigil to indicate a variable in a pattern explicitly:
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```
q is MyStruct(let a, Chrono::Trigga) then {
// a is in scope here
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}
```
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* if you have a pattern-match where one variant has a variable and the other
lacks it instead of treating this as a type error, promote the bound variable
to an option type
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* what if there was something like React jsx syntas built in? i.e. a way to
automatically transform some kind of markup into a function call, cf. `<h1
prop="arg">` -> h1(prop=arg)
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* implement and test open/use statements
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* Include extensible scala-style `html"string ${var}"` string interpolations
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* A neat idea for pattern matching optimization would be if you could match on
one of several things in a list
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ex:
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```
if x {
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is (comp, LHSPat, RHSPat) if comp in ["==, "<"] -> ...
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}
```
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* Schala should have both currying *and* default arguments!
```
fn a(b: Int, c:Int, d:Int = 1) -> Int
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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
```
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* scoped types - be able to define a quick enum type scoped to a function or other type for
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something, that only is meant to be used as a quick bespoke interface between
two other things
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ex.
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```
type enum {
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type enum MySubVariant {
SubVariant1, SubVariant2, etc.
}
Variant1(MySubVariant),
Variant2(...),
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}
```
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* inclusive/exclusive range syntax like .. vs ..=
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## Typechecking
* cf. the notation mentioned in the cardelli paper, the debug information for the `typechecking` pass should
* print the generated type variable for every subexpression in an expression
* think about idris-related ideas of multiple implementations of a type for an interface (+ vs * impl for monoids, for preorder/inorder/postorder for Foldable)
* should have an Idris-like `cast To From` function
* something like the swift `Never` type ( https://nshipster.com/never/ ) in the stdlib
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## Compilation
* look into Inkwell for rust LLVM bindings
* https://cranelift.readthedocs.io/en/latest/?badge=latest<Paste>
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* look at https://gluon-lang.org/doc/nightly/book/embedding-api.html
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# Syntax Playground
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## Trying if-syntax again
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```
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//simple if expr
if x == 10 then "a" else "z"
//complex if expr
if x == 10 then {
let a = 1
let b = 2
a + b
} else {
55
}
// different comparison ops
if x {
== 1 then "a"
.isPrime() then "b"
else "c"
}
/* for now disallow `if x == { 1 then ... }`, b/c hard to parse
//simple pattern-matching
if x is Person("Ivan", age) then age else 0
//match-block equivalent
if x {
is Person("Ivan", _) then "Ivan"
is Person(_, age) if age > 13 then "barmitzvah'd"
else "foo"
}
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```
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## (OLD) Playing around with conditional syntax ideas
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- 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" }`
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-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 '}'`