unsafe-head-exampls.ts

import { compose, toUpper } from 'ramda'

function unsafeHead<T> (list: ReadonlyArray<T>): T {
  return list[0]
}

type UpperCaseHead = (list: ReadonlyArray<string>) => string
const upperCaseHead: UpperCaseHead = compose(
  toUpper,
  unsafeHead,
) as UpperCaseHead

upperCaseHead([]) // ruh-roh:

// /Users/kcorbelli/Documents/practice-scripts/typescript/maybe/node_modules/ramda/src/invoker.js:44
//     throw new TypeError(toString(target) + ' does not have a method named "' + method + '"');
//     ^

// TypeError: undefined does not have a method named "toUpperCase"
//     at /Users/kcorbelli/Documents/practice-scripts/typescript/maybe/node_modules/ramda/src/invoker.js:44:11
//     at f1 (/Users/kcorbelli/Documents/practice-scripts/typescript/maybe/node_modules/ramda/src/internal/_curry1.js:18:17)
//     at /Users/kcorbelli/Documents/practice-scripts/typescript/maybe/node_modules/ramda/src/internal/_pipe.js:3:14
//     at /Users/kcorbelli/Documents/practice-scripts/typescript/maybe/node_modules/ramda/src/internal/_arity.js:10:19
//     at Object.<anonymous> (/Users/kcorbelli/Documents/practice-scripts/typescript/maybe/maybe.js:86:13)
//     at Module._compile (module.js:573:30)
//     at Object.Module._extensions..js (module.js:584:10)
//     at Module.load (module.js:507:32)
//     at tryModuleLoad (module.js:470:12)
//     at Function.Module._load (module.js:462:3)