[JS Compse] 4. A collection of Either examples compared to imperative code
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For if..else:
const showPage() { if(current_user) { return renderPage(current_user); } else { return showLogin(); } } const showPage() { fromNullable(current_user) .fold(showLogin, renderPage) }
const getPrefs = user => { if(user.premium) { return loadPrefs(user.preferences) } else { return defaultPrefs; } } const getPrefs = user => (user.premium ? Right(user): Left(‘not premium‘)) .map(p => user.preferences) .fold( x => defaultPrefs, x => loadPrefs(x) )
const streetName = user => { const address = user.address; if(address) { const street = address.street; if(street) { return street.name; } } return ‘no street‘; } cosnt streetName = user => fromNullable(user.address) .flatMap(address => fromNullable(address.street)) .map(street => street.name) .fold(e => ‘no street‘, n => n)
const concatUniq = (x, ys) => { const found = ys.filter(y => y === x)[0] return found ? ys : ys.concat(x); } const concatUniq = (x, ys) => fromNullable(ys.filter(y => y === x)[0]) // fromNullable needs value .fold(() => ys.concat(x), y => ys)
const wrapExamples = example => { if(example.previewPath){ try { example.preview = fs.readFileSync(example.previewPath) } catch(e) { } return example; } } const readFile = x => tryCatch(() => readFileSync(x)); const wrapExample = example => fromNullabel(exampe.previewPath) .flatMap(readFile) .fold(() => example, ex => Object.assign({preview: p}, ex); )
const parseDbUrl = cfg => { try { const c = JSON.parse(cfg); if(c.url) { return c.url.match(/..../) } catch(e) { return null } } } const parseDbUrl = cfg => tryCatch(() => JSON.parse(cfg)) .flatMap(c => fromNullable(c.url)) .fold( e => null, u => u.match(/..../) )
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json 尝试使用针对端点的此命令更新具有HL7数据的资源图层:http://resourcemap.instedd.org/api/collecti