fp-go/v2/iterator/stateless/generic/take.go

// Copyright (c) 2023 - 2025 IBM Corp.
// All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package generic

import (
	F "github.com/IBM/fp-go/v2/function"
	N "github.com/IBM/fp-go/v2/number/integer"
	O "github.com/IBM/fp-go/v2/option"
	P "github.com/IBM/fp-go/v2/pair"
)

func Take[GU ~func() O.Option[P.Pair[GU, U]], U any](n int) func(ma GU) GU {
	// pre-declare to avoid cyclic reference
	var recurse func(ma GU, idx int) GU

	fromPred := O.FromPredicate(N.Between(0, n))

	recurse = func(ma GU, idx int) GU {
		return F.Nullary3(
			F.Constant(idx),
			fromPred,
			O.Chain(F.Ignore1of1[int](F.Nullary2(
				ma,
				O.Map(P.BiMap(F.Bind2nd(recurse, idx+1), F.Identity[U])),
			))),
		)
	}

	return F.Bind2nd(recurse, 0)
}