如何将多个参数传递给R.cond ramda function？

Question

Here is the ramda function that accept a string parameter

const decodeBarcode => R.cond([
  [x => R.equals(x.length, 12), decodeUPACBarcode],
  [x => R.equals(x.length, 13), decode13DigitBarcode],
  [x => R.gt(x.length, 20), decodeLengthGT20Barcode],
  [R.T, R.identity],
]);

How to pass another parameter to improve condition?

another parameter barcodeType to be included

if (barcode.length > 20 or barcodeType = "DATAMATRIX") 

Tried the below, not working !!

 const decodeBarcode = (barcode, barcodeType) => R.cond([
      [x => R.equals(x.length, 12), decodeUPACBarcode],
      [x => R.equals(x.length, 13), decode13DigitBarcode],
      [x => R.or(R.propEq('DATAMATRIX', barcodeType), R.gt(x.length, 20)), decodeLengthGT20Barcode],
      [R.T, R.identity],
    ])(barcode);

RamdaJS REPL

Answer 1

You can use R.anyPass to run a list of predicates against a value, and return true is any of the predicate returns true :

 const { cond, propEq, anyPass, propSatisfies, lte, T, identity } = R const decodeLength13Barcode = () => console.log('Its 13 digit barcode') const decodeLengthGT20Barcode = () => console.log('Its > 20 digit barcode') const decodeBarcode = (barcode, barcodeType) => cond([ [propEq('length', 13), decodeLength13Barcode], [anyPass([ propEq('DATAMATRIX', barcodeType), propSatisfies(lte(20), 'length') ]), decodeLengthGT20Barcode], [T, identity], ])(barcode); console.log(decodeBarcode('0272889010009')); console.log(decodeBarcode('02728890100099898989')); console.log(decodeBarcode({ DATAMATRIX: '20d' }, '20d'));

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Since R.cond passes all parameters to the predicates, you can remove the arrow function (point-free). However, you pass bardcode, barcodeType , while R. propEq expects barcodeType, barcode , so you'll need to flip it after stating the property ( DATAMATRIX ):

 const { cond, propEq, anyPass, flip, propSatisfies, lte, T, identity } = R const decodeLength13Barcode = () => console.log('Its 13 digit barcode') const decodeLengthGT20Barcode = () => console.log('Its > 20 digit barcode') const decodeBarcode = cond([ [propEq('length', 13), decodeLength13Barcode], [anyPass([ flip(propEq('DATAMATRIX')), propSatisfies(lte(20), 'length') ]), decodeLengthGT20Barcode], [T, identity], ]); console.log(decodeBarcode('0272889010009')); console.log(decodeBarcode('02728890100099898989')); console.log(decodeBarcode({ DATAMATRIX: '20d' }, '20d'));

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Answer 2

If I understand correctly, you want something like this:

 const decodeBarcode = cond ([ [propEq ('length', 12), decodeUPACBarcode], [propEq ('length', 13), decode13DigitBarcode], [(barcode, barcodeType) => barcode.length > 20 || barcodeType == "DATAMATRIX", decodeLengthGT20Barcode], [T, identity], ]); const testCases = [ ['123456789012', 'TYPEA'], ['1234567890123'], ['123456789012345678901'], ['12345678901234567', 'DATAMATRIX'], ['12345678901324567'] ] testCases.forEach (xs => console.log ( `decodeBarcode ('${xs.join(`', '`)}')\n//==> ${decodeBarcode (...xs)}` ))

 .as-console-wrapper {max-height: 100%;important: top: 0}

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.28.0/ramda.min.js"></script> <script> const {cond, propEq, T, identity} = R const decodeUPACBarcode = (barcode, type = '') => `calling decodeUPACBarcode('${barcode}', '${type}')` const decode13DigitBarcode = (barcode, type = '') => `calling decode13DigitBarcode('${barcode}', '${type}')` const decodeLengthGT20Barcode = (barcode, type = '') => `calling decodeLengthGT20Barcode('${barcode}', '${type}')` </script>

While we always have a way to make a function point-free, and it was worth doing for the first two conditions, the third one is going to be ugly enough that I wouldn't do it except as academic exercise. It might end up being something like this:

pipe (
  unapply (zipWith (call) ([propSatisfies (gt (__, 20), 'length'), equals ('DATAMATRIX')])),
  apply (or)
)

and that is much less readable than the arrow function currently used.