ramda.js中带有模板字符串的Pointfree-Style

Question

I've problems writing a pointfree-style function in ramda.js and wondered if anybody can help me with that. The getEnv function reads an env-variable and logs to console if it couldn't be found.

Here is my code

const env = name => R.path(['env', name], process);

const getEnv = name => R.pipe(
  env,
  R.when(R.isNil, () => log(`Missing env "${name}"`))
)(name);

console.log(getEnv('myenv'))

I'd want to drop the name parameter of the getEnv function (and if possible also on the env function) but don't know how to do this.

Answer 1

The function getEnv does more than it should. It actualy returns the content of the path or logs a validation message .

Split it into two separate functions. In my example below, I call it findPath and validatePath , which works generically for all paths. I've wrapped validatePath into another function called validateEnvPath , which searches directly for "env"

To get rid of env you can do the following: R.flip (R.curry (R.path)) . This will turn the function curry and then the arguments around, so you can tell the function where you want to query first

 const process = {env: {myenv: ':)'}} const path = R.flip(R.curry(R.path)) const findPathInProcess = R.pipe( path (process), R.ifElse( R.isNil, R.always(undefined), R.identity ) ) const validatePath = path => validationPathResponse (findPathInProcess( path )) (`can't find something under [${path}]`) const validateEnvPath = path => validatePath (buildPath (['env']) (path)) const buildPath = xs => x => xs.concat(x) const validationPathResponse = response => errorMessage => response ? response : errorMessage console.log(validatePath(['env', 'myenv'])) console.log(validateEnvPath('myenv')) console.log(validateEnvPath('yourenv')) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script> 

Answer 2

Consider using Either monad. Sanctuary has it already implemented and plays nice with its brother ramda :

const viewEnv = S.pipe ([
    S.flip (R.append) (['env']),
    R.lensPath,
    R.view,
    S.T (process),
    S.toEither ('Given variable could not be retrieved')
])

const log = R.tap (console.log)

const eitherSomeVar = viewEnv ('someVar')
const eitherWhatever = S.bimap (log) (doSomeOtherStuff)

Answer 3

In addition one could also write the following

const path = R.flip(R.path) // already curried

const findPathInProcess = R.pipe(
  path(process),
  R.when(
    R.isNil,
    R.always(undefined)
  )
)