linguist/samples/Reason/Syntax.re

/* Copyright (c) 2015-present, Facebook, Inc. All rights reserved. */
[@@@autoFormat let wrap = 80; let shift = 2];

Modules.run ();

Polymorphism.run ();

Variants.run ();

BasicStructures.run ();

TestUtils.printSection "General Syntax";

/* Won't work! */
/* let matchingFunc a = match a with */
/*   `Thingy x => (print_string "matched thingy x"); x */
/*   | `Other x => (print_string "matched other x"); x;; */
/*  */
let matchingFunc a =>
  switch a {
  | `Thingy x =>
    print_string "matched thingy x";
    let zz = 10;
    zz
  | `Other x =>
    print_string "matched other x";
    x
  };

type firstTwoShouldBeGroupedInParens =
  (int => int) => int => int;

type allParensCanBeRemoved =
  int => int => int => int;

type firstTwoShouldBeGroupedAndFirstThree =
  ((int => int) => int) => int;

/* Same thing now but with type constructors instead of each int */
type firstTwoShouldBeGroupedInParens =
  (list int => list int) => list int => list int;

type allParensCanBeRemoved =
  list int => list int => list int => list int;

type firstTwoShouldBeGroupedAndFirstThree =
  ((list int => list int) => list int) =>
  list int;

type myRecordType = {
  firstTwoShouldBeGroupedInParens:
    (int => int) => int => int,
  allParensCanBeRemoved:
    int => int => int => int,
  firstTwoShouldBeGroupedAndFirstThree:
    ((int => int) => int) => int
};

type firstNamedArgShouldBeGroupedInParens =
  first::(int => int) => second::int => int;

type allParensCanBeRemoved =
  first::int => second::int => third::int => int;

type firstTwoShouldBeGroupedAndFirstThree =
  first::((int => int) => int) => int;

/* Same thing now, but with type constructors instead of int */
type firstNamedArgShouldBeGroupedInParens =
  first::(list int => list int) =>
  second::list int =>
  list int;

type allParensCanBeRemoved =
  first::list int =>
  second::list int =>
  third::list int =>
  list int;

type firstTwoShouldBeGroupedAndFirstThree =
  first::((list int => list int) => list int) =>
  list int;

type firstNamedArgShouldBeGroupedInParens =
  first::(int => int)? =>
  second::int list? =>
  int;

/* The arrow necessitates parens around the next two args. The ? isn't what
 * makes the parens necessary. */
type firstNamedArgShouldBeGroupedInParensAndSecondNamedArg =
  first::(int => int)? =>
  second::(int => int)? =>
  int;

type allParensCanBeRemoved =
  first::int? =>
  second::int? =>
  third::int? =>
  int;

type firstTwoShouldBeGroupedAndFirstThree =
  first::((int => int) => int) => int;

type noParens =
  one::int => int => int => two::int => int;

type noParensNeeded =
  one::int => int => int => two::int => int;

type firstNamedArgNeedsParens =
  one::(int => int => int) => two::int => int;

/* Now, let's try type aliasing */
/* Unless wrapped in parens, types between arrows may not be aliased, may not
 * themselves be arrows. */
type parensRequiredAroundFirstArg =
  (list int as 'a) => int as 'a;

type parensRequiredAroundReturnType =
  (list int as 'a) => (int as 'a);

type parensRequiredAroundReturnType =
  (list int as 'a) => (int as 'a) as 'b;

type noParensNeededWhenInTuple =
  (list int as 'a, list int as 'b) as 'entireThing;

type myTypeDef 'a = list 'a;

type instatiatedTypeDef = myTypeDef int => int;

/* Test a type attribute for good measure */
/* We should clean up all of the attribute tagging eventually, but for now,
 * let's make it super ugly to get out of the way of all the formatting/parsing
 * implementations (fewer conflicts during parsing, fewer edge cases during
 * printing).
 */
type something = (
  int,
  int [@lookAtThisAttribute]
);

type longWrappingTypeDefinitionExample =
  M_RK__G.Types.instance
    (TGRecognizer.tGFields unit unit)
    (TGRecognizer.tGMethods unit unit);

type semiLongWrappingTypeDefinitionExample =
  M_RK__Gesture.Types.instance
    TGRecognizerFinal.tGFields
    TGRecognizerFinal.tGMethods;

type semiLongWrappingTypeWithConstraint =
  M_RK__Gesture.Types.instance
    'a
    TGRecognizerFinal.tGFields
    TGRecognizerFinal.tGMethods
constraint 'a = (unit, unit);

type onelineConstrain = 'a constraint 'a = int;

/* This must be in trunk but not in this branch of OCaml */
/* type withNestedRecords = MyConstructor {myField: int} */
type colors =
  | Red int
  | Black int
  | Green int;

/* Another approach is to require declared variants to wrap any record */
/* type myRecord = MyRecord {name: int}; */
/* let myValue = MyRecord {name: int}; */
/* This would force importing of the module */
/* This would also lend itself naturally to pattern matching - and avoid having
   to use `.` operator at all since you normally destructure. */
type nameBlahType = {nameBlah: int};

let myRecord = {nameBlah: 20};

let myRecordName = myRecord.nameBlah;

let {nameBlah}: nameBlahType = {nameBlah: 20};

print_int nameBlah;

let {nameBlah: aliasedToThisVar}: nameBlahType = {
  nameBlah: 20
};

print_int aliasedToThisVar;

let desiredFormattingForWrappedLambda:
  int => int => int => nameBlahType =
  /*

   fun is
   pre-   /firstarg\
   fix   /-coupled--\
    |-\ /-to-prefix--\       */
  fun curriedArg anotherArg lastArg => {
    nameBlah: 10
  };

type longerInt = int;

let desiredFormattingForWrappedLambdaWrappedArrow:
  longerInt =>
  longerInt =>
  longerInt =>
  nameBlahType =
  /*

   fun is
   pre-   /firstarg\
   fix   /-coupled--\
    |-\ /-to-prefix--\       */
  fun curriedArg anotherArg lastArg => {
    nameBlah: 10
  };

let desiredFormattingForWrappedLambdaReturnOnNewLine
    /*

     fun is
     pre-   /firstarg\
     fix   /-coupled--\
      |-\ /-to-prefix--\       */
    curriedArg
    anotherArg
    lastArg => {
  nameBlah: 10
};

/*
 let is
 pre-
 fix    /-function binding name---\
 |-\   / is coupled to prefix      \   */
let desiredFormattingForWrappedSugar
    curriedArg
    anotherArg
    lastArg => {
  nameBlah: 10
};

/*
 let is
 pre-
 fix    /-function binding name---\
 |-\   / is coupled to prefix      \   */
let desiredFormattingForWrappedSugarReturnOnNewLine
    curriedArg
    anotherArg
    lastArg => {
  nameBlah: 10
};

/*
   let  : type t1 t2. t1 * t2 list -> t1 = ...
   let rec f : 't1 't2. 't1 * 't2 list -> 't1 =
     fun (type t1) (type t2) -> (... : t1 * t2 list -> t1)
 */
type point = {x: int, y: int};

type point3D = {x: int, y: int, z: int};

let point2D = {x: 20, y: 30};

let point3D: point3D = {
  x: 10,
  y: 11,
  z: 80 /* Optional Comma */
};

let printPoint (p: point) => {
  print_int p.x;
  print_int p.y
};

let addPoints (p1: point, p2: point) => {
  x: p1.x + p2.x,
  y: p1.y + p2.y
};

let res1 = printPoint point2D;

let res2 =
  printPoint {x: point3D.x, y: point3D.y};

/*
    When () were used to indicate sequences, the parser used seq_expr not only
    for grouping sequences, but also to form standard precedences.
                          /------- sequence_expr ------\
    let res3 = printPoint (addPoints (point2D, point3D));

    Interestingly, it knew that tuples aren't sequences.

    To move towards semi delimited, semi-terminated, braces-grouped sequences:
    while allowing any non-sequence expression to be grouped on parens, we make
    an explicit rule that allows one single non-semi ended expression to be
    grouped in parens.

    Actually: We will allow an arbitrary number of semi-delimited expressions to
    be wrapped in parens, but the braces grouped semi delimited (sequence)
    expressions must *also* be terminated with a semicolon.

    This allows the parser to distinguish between

        let x = {a};    /* Record {a:a} */
        let x = {a;};   /* Single item sequence returning identifier {a} */
 */
let res3 =
  printPoint (
    addPoints (
      point2D,
      {x: point3D.x, y: point3D.y}
    )
  );

type person = {age: int, name: string};

type hiredPerson = {
  age: string,
  name: string,
  dateHired: int
};

let o: person = {name: "bob", age: 10};

/* Parens needed? Nope! */
let o: person = {name: "bob", age: 10};

let printPerson (p: person) => {
  let q: person = p;
  p.name ^ p.name
};

/* let dontParseMeBro x y:int = x = y;*/
/* With this unification, anywhere eyou see `= fun` you can just ommit it */
let blah a => a; /* Done */

let blah a => a; /* Done (almost) */

let blah a b => a; /* Done */

let blah a b => a; /* Done (almost) */

/* More than one consecutive pattern must have a single case */
type blah = {blahBlah: int};

let blah a {blahBlah} => a;

let blah a {blahBlah} => a;

let module TryToExportTwice = {
  let myVal = "hello";
};

/*
   Unifying top level module syntax with local module syntax is probably a bad
   idea at the moment because it makes it more difficult to continue to support
   `let .. in` bindings. We can distinguish local modules for `let..in` that
   just happen to be defined at the top level (but not exported).

     let MyModule = {let myVal = 20;} in
     MyModule.x

   Wait, where would this ever be valid, even if we continued to support
   `let..in`?
 */
let onlyDoingThisTopLevelLetToBypassTopLevelSequence = {
  let x = {
    print_int 1;
    print_int 20 /* Missing trailing SEMI */
  };
  let x = {
    print_int 1;
    print_int 20; /* Ensure missing middle SEMI reported well */
    print_int 20
  };
  let x = {
    print_int 1;
    print_int 20;
    10
    /* Comment in final position */
  }; /* Missing final SEMI */
  x + x
};

type hasA = {a: int};

let a = 10;

let returnsASequenceExpressionWithASingleIdentifier
    () => a;

let thisReturnsA () => a;

let thisReturnsAAsWell () => a;

let recordVal: int = (thisReturnsARecord ()).a;

Printf.printf
  "\nproof that thisReturnsARecord: %n\n"
  recordVal;

Printf.printf
  "\nproof that thisReturnsA: %n\n"
  (thisReturnsA ());

/* Pattern matching */
let blah arg =>
  switch arg {
  /* Comment before Bar */
  | /* Comment between bar/pattern */ Red _ => 1
  /* Comment Before non-first bar */
  | /* Comment betwen bar/pattern */ Black _ => 0
  | Green _ => 0
  };

/* Any function that pattern matches a multicase match is interpretted as a
 * single arg that is then matched on. Instead of the above `blah` example:*/
let blah =
  fun
  | Red _ => 1
  | Black _ => 0
  | Green _ => 1;

/* `fun a => a` is read as "a function that maps a to a". Then the */
/* above example is read: "a function that 'either maps' Red to.. or maps .." */
/* Thc00f564e first bar is read as "either maps" */
/* Curried form is not supported:
      let blah x | Red _ => 1 | Black _ => 0;
      Theres no sugar rule for dropping => fun, only = fun
   */
/* let blahCurriedX x => fun  /* See, nothing says we can drop the => fun */ */
/*   |(Red x | Black x | Green x) => 1     /* With some effort, we can ammend the sugar rule that would */ */
/*   | Black x => 0                       /* Allow us to drop any => fun.. Just need to make pattern matching */ */
/*   | Green x => 0;                      /* Support that */ */
/*  */
let blahCurriedX x =>
  fun
  | Red x
  | Black x
  | Green x =>
    1 /* With some effort, we can ammend the sugar rule that would */
  | Black x => 0 /* Allow us to drop any => fun.. Just need to make pattern matching */
  | Green x => 0; /* Support that */

let sameThingInLocal = {
  let blahCurriedX x =>
    fun
    | Red x
    | Black x
    | Green x =>
      1 /* With some effort, we can ammend the sugar rule that would */
    | Black x => 0 /* Allow us to drop any => fun.. Just need to make pattern matching */
    | Green x => 0; /* Support that */
  blahCurriedX
};

/* This should be parsed/printed exactly as the previous */
let blahCurriedX x =>
  fun
  | Red x
  | Black x
  | Green x => 1
  | Black x => 0
  | Green x => 0;

/* Any time there are multiple match cases we require a leading BAR */
let v = Red 10;

let Black x | Red x | Green x = v; /* So this NON-function still parses */

/* This doesn't parse, however (and it doesn't in OCaml either):
     let | Black x | Red x | Green x = v;
   */
print_int x;

/* Scoping: Let sequences. Familiar syntax for lexical ML style scope and
   sequences. */
let res = {
  let a = "a starts out as";
  {
    print_string a;
    let a = 20;
    print_int a
  };
  print_string a
};

let res = {
  let a = "first its a string";
  let a = 20;
  print_int a;
  print_int a;
  print_int a
};

let res = {
  let a = "a is always a string";
  print_string a;
  let b = 30;
  print_int b
};

/* let result = LyList.map (fun | [] => true | _ => false) []; */
/* OTHERWISE: You cannot tell if a is the first match case falling through or
 * a curried first arg */
/* let blah = fun a | patt => 0 | anotherPatt => 1; */
/* let blah a patt => 0 | anotherPatt => 1; */
/*simple pattern  EQUALGREATER      expr */
let blah a {blahBlah} => a;

/*            match_case             */
/*     pattern EQUALGREATER  expr */
let blah =
  fun
  | Red _ => 1
  | Black _ => 0
  | Green _ => 0;

/* Won't work! */
/* let arrowFunc = fun a b => print_string "returning aplusb from arrow"; a + b;;  */
let arrowFunc a b => {
  print_string "returning aplusb from arrow";
  a + b
};

let add a b => {
  let extra = {
    print_string "adding";
    0
  };
  let anotherExtra = 0;
  extra + a + b + anotherExtra
};

print_string (string_of_int (add 4 34));

let dummy _ => 10;

dummy res1;

dummy res2;

dummy res3;

/* Some edge cases */
let myFun firstArg (Red x | Black x | Green x) =>
  firstArg + x;

let matchesWithWhen a =>
  switch a {
  | Red x when 1 > 0 => 10
  | Red _ => 10
  | Black x => 10
  | Green x => 10
  };

let matchesWithWhen =
  fun
  | Red x when 1 > 0 => 10
  | Red _ => 10
  | Black x => 10
  | Green x => 10;

let matchesOne (`Red x) => 10;

/*
 Typical OCaml would make you *wrap the functions in parens*! This is because it
 can't tell if a semicolon is a sequence operator. Even if we had records use
 commas to separate fields,
 */
type adders = {
  addTwoNumbers: int => int => int,
  addThreeNumbers: int => int => int => int,
  addThreeNumbersTupled: (int, int, int) => int
};

let myRecordWithFunctions = {
  addTwoNumbers: fun a b => a + b,
  addThreeNumbers: fun a b c => a + b + c,
  addThreeNumbersTupled: fun (a, b, c) =>
    a + b + c
};

let result =
  myRecordWithFunctions.addThreeNumbers 10 20 30;

let result =
  myRecordWithFunctions.addThreeNumbersTupled (
    10,
    20,
    30
  );

let lookTuplesRequireParens = (1, 2);

/* let thisDoesntParse = 1, 2;  */
let tupleInsideAParenSequence = {
  print_string "look, a tuple inside a sequence";
  let x = 10;
  (x, x)
};

let tupleInsideALetSequence = {
  print_string "look, a tuple inside a sequence";
  let x = 10;
  (x, x)
};

/* We *require* that function return types be wrapped in
   parenthesis. In this example, there's no ambiguity */
let makeIncrementer (delta: int) :(int => int) =>
  fun a => a + delta;

/* We could even force that consistency with let bindings - it's allowed
      currently but not forced.
   */
let myAnnotatedValBinding: int = 10;

/* Class functions (constructors) and methods are unified in the same way */
class classWithNoArg = {
  method x = 0;
  method y = 0;
};

/* This parses but doesn't type check
     class myClass init => object
       method x => init
       method y => init
     end;
   */
let myFunc (a: int) (b: int) :(int, int) => (
  a,
  b
);

let myFunc (a: int) (b: int) :list int => [1];

let myFunc (a: int) (b: int) :point => {
  x: a,
  y: b
};

let myFunc (a: int, b: int) :point => {
  x: a,
  y: b
};

type myThing = (int, int);

type stillARecord = {name: string, age: int};

/* Rebase latest OCaml to get the following: And fixup
   `generalized_constructor_arguments` according to master. */
/* type ('a, 'b) myOtherThing = Leaf {first:'a, second: 'b} | Null; */
type branch 'a 'b = {first: 'a, second: 'b};

type myOtherThing 'a 'b =
  | Leaf (branch 'a 'b)
  | Null;

type yourThing = myOtherThing int int;

/* Conveniently - this parses exactly how you would intend! No *need* to wrap
   in an extra [], but it doesn't hurt */
/* FIXME type lookAtThesePolyVariants = list [`Red] ; */
/* FIXME type bracketsGroupMultipleParamsAndPrecedence = list (list (list [`Red])); */
/* FIXME type youCanWrapExtraIfYouWant = (list [`Red]); */
/* FIXME type hereAreMultiplePolyVariants = list [`Red | `Black]; */
/* FIXME type hereAreMultiplePolyVariantsWithOptionalWrapping = list ([`Red | `Black]); */
/*
   /* Proposal: ES6 style lambdas: */

   /* Currying */
   let lookES6Style = (`Red x) (`Black y) => { };
   let lookES6Style (`Red x) (`Black y) => { };

   /* Matching the single argument */
   let lookES6Style = oneArg => match oneArg with
     | `Red x => x
     | `Black x => x;

   /* The "trick" to currying that we already have is basically the same - we just
    * have to reword it a bit:
    * From:
    * "Any time you see [let x = fun ...] just replace it with [let x ...]"
    * To:
    * "Any time you see [let x = ... => ] just replace it with [let x ... => ]"
    */
   let lookES6Style oneArg => match oneArg with
     | `Red x => x
     | `Black x => x;

 */

/** Current OCaml Named Arguments. Any aliasing is more than just aliasing!
    OCaml allows full on pattern matching of named args. */
/*
 A: let named              ~a    ~b                = aa + bb in
 B: let namedAlias         ~a:aa ~b:bb             = aa + bb in
 C: let namedAnnot         ~(a:int) ~(b:int)       = a + b in
 D: let namedAliasAnnot    ~a:(aa:int) ~b:(bb:int) = aa + bb in
 E: let optional           ?a    ?b                              = 10 in
 F: let optionalAlias      ?a:aa ?b:bb                           = 10 in
 G: let optionalAnnot      ?(a:int option) ?(b:int option)       = 10 in
 H: let optionalAliasAnnot ?a:(aa:int option) ?b:(bb:int option) = 10 in
 /*
 Look! When a default is provided, annotation causes inferred type of argument
 to not be "option" since it's automatically destructured (because we know it
 will always be available one way or another.)
 */
 I: let defOptional           ?(a=10)    ?(b=10)                 = 10 in
 J: let defOptionalAlias      ?a:(aa=10) ?b:(bb=10)              = 10 in
 K: let defOptionalAnnot      ?(a:int=10) ?(b:int=10)            = 10 in
                             \       \
                              \label_let_pattern opt_default: no longer needed in SugarML

 L: let defOptionalAliasAnnot ?a:(aa:int=10) ?b:(bb:int=10)      = 10 in
                               \        \
                                \let_pattern: still a useful syntactic building block in SugarML
 */

/**
 * In Reason, the syntax for named args uses double semicolon, since
 * the syntax for lists uses ES6 style [], freeing up the ::.
 */
let a = 10;

let b = 20;

/*A*/
let named a::a b::b => a + b;

type named = a::int => b::int => int;

/*B*/
let namedAlias a::aa b::bb => aa + bb;

let namedAlias a::aa b::bb => aa + bb;

type namedAlias = a::int => b::int => int;

/*C*/
let namedAnnot a::(a: int) b::(b: int) => 20;

/*D*/
let namedAliasAnnot a::(aa: int) b::(bb: int) => 20;

/*E*/
let myOptional a::a=? b::b=? () => 10;

type named = a::int? => b::int? => unit => int;

/*F*/
let optionalAlias a::aa=? b::bb=? () => 10;

/*G*/
let optionalAnnot a::(a: int)=? b::(b: int)=? () => 10;

/*H*/
let optionalAliasAnnot
    a::(aa: int)=?
    b::(bb: int)=?
    () => 10;

/*I: */
let defOptional a::a=10 b::b=10 () => 10;

type named = a::int? => b::int? => unit => int;

/*J*/
let defOptionalAlias a::aa=10 b::bb=10 () => 10;

/*K*/
let defOptionalAnnot
    a::(a: int)=10
    b::(b: int)=10
    () => 10;

/*L*/
let defOptionalAliasAnnot
    a::(aa: int)=10
    b::(bb: int)=10
    () => 10;

/*M: Invoking them - Punned */
let resNotAnnotated = named a::a b::b;

/*N:*/
let resAnnotated: int = named a::a b::b;

/*O: Invoking them */
let resNotAnnotated = named a::a b::b;

/*P: Invoking them */
let resAnnotated: int = named a::a b::b;

/*Q: Here's why "punning" doesn't work!  */
/* Is b:: punned with a final non-named arg, or is b:: supplied b as one named arg? */
let b = 20;

let resAnnotated = named a::a b::b;

/*R: Proof that there are no ambiguities with return values being annotated */
let resAnnotated: ty = named a::a b;

/*S: Explicitly passed optionals are a nice way to say "use the default value"*/
let explictlyPassed =
  myOptional a::?None b::?None;

/*T: Annotating the return value of the entire function call */
let explictlyPassedAnnotated: int =
  myOptional a::?None b::?None;

/*U: Explicitly passing optional with identifier expression */
let a = None;

let explictlyPassed = myOptional a::?a b::?None;

let explictlyPassedAnnotated: int =
  myOptional a::?a b::?None;

let nestedLet = {
  let _ = 1;
  ()
};

let nestedLet = {
  let _ = 1;
  ()
};

let nestedLet = {
  let _ = 1;
  ()
};

let nestedLet = {
  let _ = 1;
  2
};

/*
 * Showing many combinations of type annotations and named arguments.
 */
type typeWithNestedNamedArgs =
  outerOne::(
    innerOne::int => innerTwo::int => int
  ) =>
  outerTwo::int =>
  int;

type typeWithNestedOptionalNamedArgs =
  outerOne::
    (innerOne::int => innerTwo::int => int)? =>
  outerTwo::int? =>
  int;

type typeWithNestedOptionalNamedArgs =
  outerOne::list string? => outerTwo::int? => int;

let x =
  callSomeFunction
    withArg::10 andOtherArg::wrappedArg;

let res = {
  (constraintedSequenceItem: string);
  (dontKnowWheYoudWantToActuallyDoThis: string)
};

let res = {
  (
    butTheyWillBePrintedWithAppropriateSpacing: string
  );
  (soAsToInstillBestDevelopmentPractices: string)
};

let x = [
  (eachItemInListCanBeAnnotated: int),
  (typeConstraints: float),
  (
    tupleConstraints: int,
    andNotFunctionInvocations: int
  )
];

let x = [
  (butWeWillPrint: int),
  (themAsSpaceSeparated: float),
  (toInfluenceYour: int, developmentHabbits: int)
];

let newRecord = {
  ...(annotatedSpreadRecord: someRec),
  x: y
};

let newRecord = {
  ...(annotatedSpreadRecord: someRec),
  blah: 0,
  foo: 1
};

let newRecord = {
  ...(
    youCanEvenCallMethodsHereAndAnnotate them: someRec
  ),
  blah: 0,
  foo: 1
};

let newRecord = {
  ...(
    youCanEvenCallMethodsHereAndAnnotate
      them named::10: someRec
  ),
  blah: 0,
  foo: 1
};

let something: thing blah = aTypeAnnotation;

let something: thing blah = thisIsANamedArg;

let something: thing blah = aTypeAnnotation;

let something: blah = thisIsANamedArg thing;

let something: blah = typeAnnotation thing;

let newRecord = {
  ...(
    heresAFunctionWithNamedArgs argOne::i: annotatedResult
  ),
  soAsToInstill: 0,
  developmentHabbits: 1
};

[@@@thisIsAThing];

let x = 10;

/* Ensure that the parenthesis are preserved here because they are
 * important:
 */
let something =
  fun
  | None => (
      fun
      | [] => "emptyList"
      | [_, ..._] => "nonEmptyList"
    )
  | Some _ => (
      fun
      | [] => "emptyList"
      | [_, ..._] => "nonEmptyList"
    );

/*  A | B = X; */
let A | B = X;

/*  A | (B | C) = X; */
let A | (B | C) = X;

/* (A | B) | (C | D) = X; */
let A | B | (C | D) = X;

/*  A | B | (C | D) = X; */
let A | B | (C | D) = X;

/* (A | B) | C = X; */
let A | B | C = X;

/*  A | B | C = X; */
let A | B | C = X;


/** External function declaration
 *
 */
external f : int => int = "foo";

let x = {contents: 0};

let unitVal = x.contents = 210;