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+ SeqT.head and SeqT.tryHead #609

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Merged
gusty merged 2 commits into from
Jun 8, 2025
Merged

+ SeqT.head and SeqT.tryHead #609

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b953a0e
+ SeqT.head and SeqT.tryHead
gusty Oct 8, 2024
3ab768c
Merge branch 'master' into gus/seqt-head
gusty Nov 11, 2024
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8 changes: 8 additions & 0 deletions src/FSharpPlus/Data/Seq.fs
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Expand Up @@ -764,6 +764,14 @@ module SeqT_V2 =
let inline iteri<'T, .. > (f: int -> 'T -> unit) (source: SeqT<'``Monad<bool>``, 'T>) : '``Monad<unit>`` = iteriM (fun i x -> result (f i x)) source
let inline iter<'T, .. > f (source: SeqT<'``Monad<bool>``, 'T>) : '``Monad<unit>`` = iterM (f >> result) source

let inline tryHead (source: SeqT<'``Monad<bool>``, 'T>) : '``Monad<'T option>`` =
use ie = (source :> IEnumerableM<'``Monad<bool>``, 'T>).GetEnumerator ()
Bind.Invoke (ie.MoveNext ()) (fun b -> Return.Invoke (if b then Some ie.Current else None))

let inline head (source: SeqT<'``Monad<bool>``, 'T>) : '``Monad<'T>`` =
use ie = (source :> IEnumerableM<'``Monad<bool>``, 'T>).GetEnumerator ()
Bind.Invoke (ie.MoveNext ()) (fun b -> Return.Invoke (if b then ie.Current else invalidArg (nameof source) "The input sequence was empty."))

let inline internal tryPickMAndMap<'T, 'U, .. > (f: 'T -> '``Monad<'U option>``) (source: SeqT<'``Monad<bool>``, 'T>) (postMap: 'U option -> 'V) : '``Monad<'V>`` = innerMonad2<_, '``Monad<unit>``> () {
use ie = (source :> IEnumerableM<'``Monad<bool>``, 'T>).GetEnumerator ()
let! move = ie.MoveNext ()
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