{-# LANGUAGE OverloadedStrings #-}

module Funcons.Core.Values.Composite.Collections.TuplesBuiltin where

import Funcons.EDSL
import Funcons.Types

library = libFromList [
        ("discard-empty-tuples", ValueOp discard_empty_tuples_op)
    ,   ("tuple-index", ValueOp stepTupleIndex)
    ]

discard_empty_tuples_ = FApp "discard-empty-tuples" . FTuple
discard_empty_tuples_op vs = rewriteTo $ FValue $ safe_tuple_val (filter (/= EmptyTuple) vs)

-- | /tuple-index(_,N)/ selects the /N/th component of a tuple.
--   e.g. /tuple-index((true,"hello",'B'),2)/ = `"hello"
tuple_index_ :: [Funcons] -> Funcons
tuple_index_ = applyFuncon "tuple-index"

stepTupleIndex args@[NonEmptyTuple v1 v2 vs, vn]
    | Nat n <- upcastNaturals vn =
       let vals = v1:v2:vs
           i    = fromInteger n
        in if i > 0 && i <= length vals
              then rewriteTo (FValue (vals !! (i-1)))
              else partialOp (tuple_index_ (fvalues args)) "index out of range"
stepTupleIndex args = sortErr (tuple_index_ (fvalues args)) "tuple-index must be applied to a (non-empty) tuple and a natural number"