jrsinclair

function processRow(headerFields, row) {
    const fieldsEither   = right(row).map(splitFields);
    const rowObj         = fieldsEither.map(zipRow(headerFields));
    // ... But now we have another problem ...
}

jrsinclair

function zipRow(headerFields) {
    return function zipRowWithHeaderFields(fieldData) {
        const lengthMatch = (headerFields.length == fieldData.length);
        return (!lengthMatch)
            ? left(new Error("Row has an unexpected number of fields"))
            : right(_.zipObject(headerFields, fieldData));
    };
}

jrsinclair

function processRow(headerFields, row) {
    const fieldsEither   = right(row).map(splitFields);
    const rowObj         = fieldsEither.map(zipRow /* wait. this isn't right */);
    // ...
}

jrsinclair

function processRow(headerFields, row) {
    const fieldsEither   = right(row).map(splitFields);
   // …
}

jrsinclair

function zipRow(headerFields, fieldData) {
    const lengthMatch = (headerFields.length == fieldData.length);
    return (!lengthMatch)
        ? left(new Error("Row has an unexpected number of fields"))
        : right(_.zipObject(headerFields, fieldData));
}

function addDateStr(messageObj) {
    const errMsg = 'Unable to parse date stamp in message object';

jrsinclair

function left(x) {
    return Left.of(x);
}

function right(x) {
    return Right.of(x);
}

jrsinclair

Left.of = function of(x) {
    return new Left(x);
};

jrsinclair

const leftHello        = new Left('Hello world');
const rightHello       = new Right('Hello world');
const worldToLogRocket = str => str.replace(/world/, 'LogRocket');

leftHello.map(worldToLogRocket).map(trace);
// Doesn't print any thing to the console
// ￩ Left(Hello world)

rightHello.map(worldToLogRocket).map(trace);
// ⦘ Hello LogRocket

jrsinclair

/**
 * Left represents the sad path.
 */
class Left {
    constructor(val) {
        this._value = val;
    }

    map() {
        // Left is the sad path

jrsinclair

const leftHello  = new Left('Hello world');
const rightHello = new Right('Hello world');

leftHello.runFunctionOnlyOnHappyPath(trace);
// does nothing


rightHello.runFunctionOnlyOnHappyPath(trace);
// ⦘ Hello world
// ￩ "Hello world"