Skip to content

use maybes for unsafe operations #683

Closed
@davidchambers

Description

@davidchambers

Certain Ramda functions are unsafe. Take this quartet, for example:

R.head :: [a] -> a | Undefined  -- unsafe
R.last :: [a] -> a | Undefined  -- unsafe
R.tail :: [a] -> [a]            -- safe, but misleading
R.init :: [a] -> [a]            -- safe, but misleading

I suggest the following types:

R.head :: [a] -> Maybe a
R.last :: [a] -> Maybe a
R.tail :: [a] -> Maybe [a]
R.init :: [a] -> Maybe [a]

We could also provide the unsafe versions:

R.unsafeHead :: [a] -> a | Undefined
R.unsafeLast :: [a] -> a | Undefined
R.unsafeTail :: [a] -> [a]
R.unsafeInit :: [a] -> [a]

We'd also provide the following function which takes a default value as its first argument:

R.fromMaybe :: a -> Maybe a -> a

Let's consider a simple example: taking the first element of a [String] of unknown length and converting it to upper-case.

// Naive solution (will throw if list is empty)
R.toUpper(R.head(list))

// Pre-emptive check
R.ifElse(R.isEmpty, R.always('<default>'), R.pipe(R.head, R.toUpperCase))(list)

// Maybe
R.fromMaybe('<default>', R.map(R.toUpperCase, R.head(list)))

It's cleaner and less error-prone to map over a maybe than to rely on checking for the empty list whenever one uses a member of this quartet.

These types are used by purescript-arrays. I'd like to Ramda do the same.

Metadata

Metadata

Assignees

No one assigned

    Labels

    No labels
    No labels

    Type

    No type

    Projects

    No projects

    Milestone

    No milestone

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions