Invoking primitive operators in non-JS backends

thautwarm · February 18, 2020, 3:14pm

I’m now using a non-JS backend, where Prelude is not available yet.

Things are a bit troublesome because it seems that I can only use function calls to achieve primitive operators now,

For instance, when I want to make a negative number, I have to implement negate, and it seems that I have to use a foreign function and cannot inline it:

github.com

Testing-PureScript-Python/pattern-matching/blob/master/src/SmallPrelude.purs#L8


module SmallPrelude where


data IO a


foreign import println :: forall a. a -> IO {}
foreign import discard :: forall a b. IO a -> (a -> IO b) -> IO b
foreign import iadd :: Int -> Int -> Int
foreign import negate :: Int -> Int
foreign import error :: String -> forall a. a
foreign import igt :: Int -> Int -> Boolean

github.com

Testing-PureScript-Python/pattern-matching/blob/master/src/Main.purs#L21


natToInt (Succ a) = 1 `iadd` natToInt a


natToIntRecImpl :: Int -> Nat -> Int
natToIntRecImpl a Zero = a
natToIntRecImpl r (Succ a) = natToIntRecImpl (1 `iadd` r) a


natToIntRec = natToIntRecImpl 0


intToNatRecImpl :: Nat -> Int -> Nat
intToNatRecImpl a 0 = a
intToNatRecImpl a n = intToNatRecImpl (Succ a) (n `iadd` -1)


intToNatRec n
  | n `igt` 0        = error ""
  | true             = intToNatRecImpl Zero n


_3 = Succ (Succ (Succ Zero))


-- test deconstructions in guards
testDeconsGuard n
  | Succ a <- n = false

I wonder if there’re any approches for inlining those primitive function calls.

natefaubion · February 18, 2020, 3:30pm

In the current compiler this is done as part of backend code generation. The backend needs to match on a specific identifier and generate the inlined code instead (much like how GHC has the GHC.PrimOps namespace).

thautwarm · February 18, 2020, 4:42pm

Got it. So do we have a documentation page listing out the namespaces providing inline-able functions?

natefaubion · February 18, 2020, 5:12pm

The namespaces are whatever the backend supports. The JS backend inlines stuff from Prelude.

thautwarm · February 18, 2020, 7:28pm

I want to follow the existing JS conventions, because I want to use the existing codebase.

natefaubion · February 18, 2020, 7:39pm

github.com

purescript/purescript/blob/ed130c78b708ff55cf4a80b126a1bd3ba5d80eb9/src/Language/PureScript/CoreImp/Optimizer/Inliner.hs#L84-L172


inlineCommonValues :: AST -> AST
inlineCommonValues = everywhere convert
  where
  convert :: AST -> AST
  convert (App ss fn [dict])
    | isDict' [semiringNumber, semiringInt] dict && isDict fnZero fn = NumericLiteral ss (Left 0)
    | isDict' [semiringNumber, semiringInt] dict && isDict fnOne fn = NumericLiteral ss (Left 1)
    | isDict boundedBoolean dict && isDict fnBottom fn = BooleanLiteral ss False
    | isDict boundedBoolean dict && isDict fnTop fn = BooleanLiteral ss True
  convert (App ss (App _ fn [dict]) [x])
    | isDict ringInt dict && isDict fnNegate fn = Binary ss BitwiseOr (Unary ss Negate x) (NumericLiteral ss (Left 0))
  convert (App ss (App _ (App _ fn [dict]) [x]) [y])
    | isDict semiringInt dict && isDict fnAdd fn = intOp ss Add x y
    | isDict semiringInt dict && isDict fnMultiply fn = intOp ss Multiply x y
    | isDict ringInt dict && isDict fnSubtract fn = intOp ss Subtract x y
  convert other = other
  fnZero = (C.dataSemiring, C.zero)
  fnOne = (C.dataSemiring, C.one)
  fnBottom = (C.dataBounded, C.bottom)
  fnTop = (C.dataBounded, C.top)

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