fp-go/internal/file/resource.go

package file

import (
	F "github.com/ibm/fp-go/function"
)

// WithResource constructs a function that creates a resource, then operates on it and then releases the resource
func WithResource[
	GA,
	GR,
	GANY,
	E, R, A, ANY any](
	mchain func(GR, func(R) GA) GA,
	mfold1 func(GA, func(E) GA, func(A) GA) GA,
	mfold2 func(GANY, func(E) GA, func(ANY) GA) GA,
	mmap func(GANY, func(ANY) A) GA,
	left func(E) GA,
) func(onCreate func() GR, onRelease func(R) GANY) func(func(R) GA) GA {

	return func(onCreate func() GR, onRelease func(R) GANY) func(func(R) GA) GA {

		return func(f func(R) GA) GA {
			return mchain(
				onCreate(), func(r R) GA {
					// handle errors
					return mfold1(
						f(r),
						func(e E) GA {
							// the original error
							err := left(e)
							// if resource processing produced and error, still release the resource but return the first error
							return mfold2(
								onRelease(r),
								F.Constant1[E](err),
								F.Constant1[ANY](err),
							)
						},
						func(a A) GA {
							// if resource processing succeeded, release the resource. If this fails return failure, else the original error
							return F.Pipe1(
								onRelease(r),
								F.Bind2nd(mmap, F.Constant1[ANY](a)),
							)
						})
				},
			)
		}
	}
}