MapWith alternatives and similar packages
Based on the "Combinators" category.
Alternatively, view MapWith alternatives based on common mentions on social networks and blogs.
Do you think we are missing an alternative of MapWith or a related project?
fmap, but can "inject" additional parameters such as whether first (or last) element, etc.
I often want to map over a list, but do something slightly different with the first or last element.
For a long time I used markbounds, but also wanted something that:
- works on structures other than lists (
mapWithworks on all
- can provide additional types of parameter (not just first/last), such as:
- index from start/end;
- the previous/next element; and
- makes it easy to create new types of parameter to provide; and
- can provide any number of separate parameters to a function (not just a 3-tuple).
So, after only 2 years, I built a small library to do all of these.
Passing a "standard combination" of isFirst and isLast parameters:
let g x f l = [star f, x, star l]; star b = if b then '*' else ' ' in withFirstLast g "fred" ["*f ", " r ", " e ", " d*"]
Passing a custom combination of different types of parameter (the index from the start, whether it's the last element, and elements from another list applied from the right):
let g x n l e = concat [[x], show n, if l then "*" else "-", e] in mapWith (g ^-> eltIx & isLast <-^ eltFrom ["x","yy","z","zzzz","y"]) "fred" ["f0-zzzz","r1-z","e2-yy","d3*x"]
More examples are here.
Note that this is my first library and my first use of cabal, so I've probably done some dumb things.
Some things I wonder:
- Doesn't this already exist? (It feels like it should!)
- Should I name it
Data.Traversable.MapWith? Or are such names "reserved" for "official" libraries, or something? Would this name impact my own file/directory structures?
Areas for potential improvement in later releases:
Performance investigations and hopefully improvements, in particular:
- fusion for eltFrom Injectors (unlikely, given the reasons it's not possible for zipWith, but we'll see).
- enhancements for "stateful" "from the right" Injectors (unlikely, given this).
CurryTF: avoid tuples? (The tuple
(7, ())is interpreted by
CurryTFas an application of a single value
7, but by
Data.Tuple.Curryas two values:
(), which I think is slightly more confusing than it needs to be.)