91 lines
3.4 KiB
Plaintext
91 lines
3.4 KiB
Plaintext
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#v3
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# Added type aliases.
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# Added some row variable examples.
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# Added array type
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# TODO Add optional types
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# TODO Get rid of ambiguous syntax at end of type alias definition.
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# TODO Try out arbitrary strings as field names
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# This should be fine without any extra syntax, as long as we don't allow pattern-matching primitive values.
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# For consistency, especially re: punning, we'd need to also allow this for normal identifiers, which would need
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# new syntax.
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# TODO Modules (files) and opaque types
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# TODO More primitive types
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# v2
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# I realized/remembered that I don't need `def`, `and`, or commas. Because function
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# application isn't by juxtapositon, I can look ahead by one token to know
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# whether the expression is complete.
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# If the language is impure, it also needs a sequencing operator. Let's use ;
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# because why not?
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type alias tree 'a = recurse 'T in <leaf, branch: {left: 'T, value: 'a, right: 'T}>
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type alias maybe 'a = <some: 'a, nothing>
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type alias unit = {}
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binary_tree : fn('a, 'a) -> {
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empty: tree 'a,
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insert: fn(tree 'a, 'a) -> tree 'a,
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find: fn(tree 'a, 'a) -> maybe 'a,
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func_we_dont_care_about: fn() -> unit
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}
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# Type aliases should appear in compiler messages.
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# binary_tree takes a comparison function and returns a record (like a JS
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# object) as a module for handling binary trees of values of the same type
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# as compare's arguments.
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binary_tree(compare) =
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# Backticks here indicate that leaf is a constructor for a tagged union
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# (variant) type.
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let
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# A let expression can bind multiple names. Functions have access to all names within the expression,
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# while other values only have access to names bound before them.
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# This is to prevent nonsensical mutual recursion between non-function values.
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empty = `leaf
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insert(tree, value) = when tree is
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`leaf => `branch({left=`leaf, value = value, right=`leaf)
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`branch({left, value=value2, right}) => when compare(value, value2) is
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`eq => `branch({left, value, right})
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`lt =>
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let new_left = insert(left, value)
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in `branch({left=new_left, value=value2, right})
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`gt =>
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let new_right = insert(right, value)
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in `branch({left, value=value2, new_right})
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find(tree, needle) = when tree is
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`leaf => `nothing
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`branch({left, value, right}) => when compare(needle, value) is
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`eq => `some(value)
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`lt => find(left, needle)
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`gt => find(right, needle)
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func_we_dont_care_about() = print("ignore me")
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in {empty, insert, find}
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# Prints "`some(2)".
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do_tree_things() =
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# Assume that int_compare is in the stdlib or something.
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# Notice that we can ignore a record field. I want to make record
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# syntax basically the same as in JS.
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let {insert, empty, find | stuff_we_dont_need} = binary_tree(int_compare)
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# I invented this fancy partial-application syntax with _, and then found
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# that Scala does it the same way. Also note the pipe operator from Elm.
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in
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empty |> insert(_, 5) |> insert(_, 2) |> insert(_, 10)
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|> find(2) |> print;
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stuff_we_dont_need
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# Prints "`some(2)\nignore me".
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main() = do_tree_things().func_we_dont_care_about()
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annotate: fn('a, {|'b}) -> {note: 'a | 'b}
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annotate(note, obj) = { note | obj }
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deannotate: fn({note: 'a | 'b}) -> {|'b}
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deannotate(r) = let {note=_ | rest} = r in rest
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reannotate: fn('a, {note: 'a | 'b}) -> {note: 'a | 'b}
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reannotate(note, obj) = {|obj with note=note} # or maybe field punning: {|obj with note}
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map: fn(fn('a) -> 'b, ['a]) -> ['b]
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doubled = let double(n) = 2 * n in map(double, [1,2,3,4,5])
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