Composable decoders

[dearlordylord]

I think it's related to "S.merge" accepting only plain object schemas (e.g no unions, no primitives):

const integerSchema = S.refine(S.number, (value, s) => {
  if (value % 1 !== 0) {
    throw s.fail('Must be an integer');
  }
});

const nonNegativeNumberSchema = S.refine(S.number, (value, s) => {
  if (value < 0) {
    throw s.fail('Must be a positive number');
  }
});

// have to repeat, I didn't find a way to combine integerSchema and nonNegativeNumberSchema
// e.g. S.merge() works only with objects
const nonNegativeIntegerSchema = S.refine(integerSchema, (value, s) => {
  if (value < 0) {
    throw s.fail('Must be a positive number');
  }
});

[dearlordylord]

ref #60

[DZakh]

I already have plans for v9 and probably won't have time adding the feature in the near future. As for workaround I'd suggest move the refine into a reusable function:

const toNonNegativeNumberSchema = schema => S.refine(schema, (value, s) => {
  if (value < 0) {
    throw s.fail('Must be a positive number');
  }
});

const nonNegativeIntegerSchema = toNonNegativeNumberSchema(integerSchema)

Also, there are built-in S.integer and S.numberMin(S.number, 0) you can use https://github.com/DZakh/rescript-schema/blob/main/docs/js-usage.md#numbers.