Expression Trees: Syntax Supported
Expression tree DSLs can use most of the expression and statement syntax in Hack.
For a full list of supported syntax, see also expr_tree.hhi.
Literals
| Example | Visitor Runtime | Typing |
|---|---|---|
true |
$v->visitBool($position, true) |
MyDsl::boolType() |
1 |
$v->visitInt($position, 1) |
MyDsl::intType() |
1.23 |
$v->visitFloat($position, 1.23) |
MyDsl::floatType() |
"foo" |
$v->visitString($position, "foo") |
MyDsl::stringType() |
null |
$v->visitString($position) |
MyDsl::nullType() |
| N/A | N/A | MyDsl::voidType() |
Binary Operators
Operator names are based on the appearance of the symbol, as different DSLs may choose different semantics for an operator.
| Example | Visitor Runtime | Typing |
|---|---|---|
$x + $y |
$v->visitBinop($position, ..., '__plus', ...) |
__plus method on $x |
$x - $y |
$v->visitBinop($position, ..., '__minus', ...) |
__minus method on $x |
$x * $y |
$v->visitBinop($position, ..., '__star', ...) |
__star method on $x |
$x / $y |
$v->visitBinop($position, ..., '__slash', ...) |
__slash method on $x |
$x % $y |
$v->visitBinop($position, ..., '__percent', ...) |
__percent method on $x |
$x && $y |
$v->visitBinop($position, ..., '__ampamp', ...) |
__ampamp method on $x |
$x || $y |
$v->visitBinop($position, ..., '__barbar', ...) |
__barbar method on $x |
$x < $y |
$v->visitBinop($position, ..., '__lessThan', ...) |
__lessThan method on $x |
$x <= $y |
$v->visitBinop($position, ..., '__lessThanEqual', ...) |
__lessThanEqual method on $x |
$x > $y |
$v->visitBinop($position, ..., '__greaterThan', ...) |
__greaterThan method on $x |
$x >= $y |
$v->visitBinop($position, ..., '__greaterThanEqual', ...) |
__greaterThanEqual method on $x |
$x === $y |
$v->visitBinop($position, ..., '__tripleEquals', ...) |
__tripleEquals method on $x |
$x !== $y |
$v->visitBinop($position, ..., '__notTripleEquals', ...) |
__notTripleEquals method on $x |
$x . $y |
$v->visitBinop($position, ..., '__dot', ...) |
__dot method on $x |
$x & $y |
$v->visitBinop($position, ..., '__amp', ...) |
__amp method on $x |
$x | $y |
$v->visitBinop($position, ..., '__bar', ...) |
__bar method on $x |
$x ^ $y |
$v->visitBinop($position, ..., '__caret', ...) |
__caret method on $x |
$x << $y |
$v->visitBinop($position, ..., '__lessThanLessThan', ...) |
__lessThanLessThan method on $x |
$x >> $y |
$v->visitBinop($position, ..., '__greaterThanGreaterThan', ...) |
__greaterThanGreaterThan method on $x |
Ternary Operators
| Example | Visitor Runtime | Typing |
|---|---|---|
$x ? $y : $z |
$v->visitTernary($position, ..., ..., ...) |
$x->__bool() ? $y : $z |
Unary Operators
| Example | Visitor Runtime | Typing |
|---|---|---|
!$x |
$v->visitUnop($position, ..., '__exclamationMark') |
__exclamationMark method on $x |
-$x |
$v->visitUnop($position, ..., '__negate') |
__negate method on $x |
~$x |
$v->visitUnop($position, ..., '__tilde') |
__tilde method on $x |
$x++ |
$v->visitUnop($position, ..., '__postfixPlusPlus') |
__postfixPlusPlus method on $x |
$x-- |
$v->visitUnop($position, ..., '__postfixMinusMinus') |
__postfixMinusMinus method on $x |
Local Variables
| Example | Visitor Runtime | Typing |
|---|---|---|
$x |
$v->visitLocal($position, '$x') |
Same as normal Hack |
You can see here that the visitor runtime does not know the type of $x, it
just sees a call to visitLocal with the variable name as a string
'$x'.
Note that expression trees do not allow free variables. You can only use local variables that have been previously assigned or introduced with a lambda.
Lambdas
| Example | Visitor Runtime | Typing |
|---|---|---|
(Foo $x) ==> $y |
$v->visitLambda($position, vec['$x'], vec[...]) |
Same as normal Hack |
Note that the visitor runtime does not see the type of $x.
Statements
| Example | Visitor Runtime | Typing |
|---|---|---|
$x = $y; |
$v->visitAssign($position, ..., ...) |
Same as normal Hack |
return $x; |
$v->visitReturn($position, ...) |
Same as normal Hack |
return; |
$v->visitReturn($position, null) |
Same as normal Hack |
if (...) {...} else {...} |
$v->visitIf($position, ..., ..., ...) |
if (...->__bool()) {...} else {...} |
while (...) {...} |
$v->visitWhile($position, ..., vec[...]) |
while (...->__bool()) {...} |
for (...; ...; ...) {...} |
$v->visitFor($position, vec[...], ..., vec[...], vec[...]) |
for (...; ...->__bool(); ...) {...} |
break; |
$v->visitBreak($position) |
Same as normal Hack |
continue; |
$v->visitContinue($position) |
Same as normal Hack |
Calls
| Example | Visitor Runtime | Typing |
|---|---|---|
foo(...) |
$v->visitCall($position, $v->visitGlobalFunction($position, foo<>), vec[...]) |
MyDsl::symbolType(foo<>)() |
Foo::bar(...) |
$v->visitCall($position, $v->visitStaticMethod($position, Foo::bar<>), vec[...]) |
MyDsl::symbolType(Foo::bar<>)() |
Note that the function or method must have a Hack definition, so the typechecker can verify that it's being called with appropriate arguments.
XHP Literals
| Example | Visitor Runtime | Typing |
|---|---|---|
<foo ...>...</foo> |
$v->visitXhp($position, :foo::class, dict[...], vec[...]) |
<foo ...>...</foo> |
Property Access
| Example | Visitor Runtime | Typing |
|---|---|---|
(...)->foo |
$v->visitPropertyAccess($position, ..., 'foo') |
(...)->foo |
Splicing
| Example | Visitor Runtime | Typing |
|---|---|---|
${$x} |
$v->splice($position, 'key0', $x) |
Extract the inferred type out of the third type argument of Spliceable |
Unsupported Features
Expression trees may only contain expressions between the backticks.
MyDsl`1`; // OK: 1 is an expression
MyDsl`while(true) {}`; // Bad: statement
MyDsl`() ==> { while true() {} }`; // OK: statements are allowed in lambdas
MyDsl`class Foo {}`; // Bad: top-level declaration.
Thank You!
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