`evolve` throws while absent of corresponding transformations

[imcotton]

🐛 Bug report

Current Behavior

evolve from struct throws while having absent transformations:

node_modules/fp-ts/lib/struct.js:78
            out[k] = transformations[k](a[k]);
                                       ^

TypeError: transformations[k] is not a function
    at node_modules/fp-ts/lib/struct.js:78:40

Expected behavior

Leaves unspecified entries untouched.

Reproducible example

const { pipe, identity } = require('fp-ts/function')
const { singleton } = require('fp-ts/ReadonlyRecord')
const { evolve } = require('fp-ts/struct')

// Expected { a: 1 }
const result = pipe(
    singleton('a', 1),
    evolve({
        b: identity,
    }),
)

Suggested solution(s)

Check before invoking transformations.

Additional context

Expected behavior would align with the evolve from Ramda as well.

Your environment

Did this work in previous versions of fp-ts? no

Which versions of fp-ts are affected by this issue?

Software	Version(s)
fp-ts	2.11 2.12
TypeScript	4.7



[danielo515]

Ok, happy to see that I'm not the only one with this expectation. In fact, I expected the transformation struct to drive the logic completely, so all the functions are executed even if the passed value doesn't contain one of the keys (which TS should probably detect anyway).

Please note this is a problem because the structural typing nature of typescript, where you can pass extra properties without any type error, and this will fail at runtime.