Q&A: coming from Ramda or fp-ts?

[roxdavirox]

If you are migrating from Ramda, fp-ts, or lodash/fp, ask your questions here.

Common mappings

From Ramda

Ramda	fp-core
R.pipe(f, g)(x)	pipe(x, f, g)
R.compose(f, g)	compose(f, g)
R.map(fn, list)	map(fn)(list)
R.filter(pred, list)	filter(pred)(list)
R.groupBy(fn, list)	groupBy(fn)(list)
R.either(f, g)	or(f, g) (predicates)
R.both(f, g)	and(f, g) (predicates)
R.memoizeWith	memoize(fn, keyFn)

From fp-ts

fp-ts	fp-core
Either<E, A>	Result<T, E>
Option<A>	Option<T>
right(a)	Ok(a)
left(e)	Err(e)
some(a)	Some(a)
none	None
pipe(x, E.map(f))	pipe(x, mapResult(f))
pipe(x, E.chain(f))	pipe(x, flatMap(f))

Key differences

• pipe is value-first: pipe(value, fn1, fn2) not pipe(fn1, fn2)(value)
• No HKT machinery: fp-core does not use higher-kinded types — simpler types, no Kind<F, A>
• No category theory naming: flatMap not chain, match not fold

Post your questions below.