[Javascript Crocks] Recover from a nothing with the ' coalesce ' Method

altThe method allows us to recover from a nothing with a default maybe, but sometimes our recovery efforts might need t o Enlist some logic to recover properly. In this lesson, we'll see how we can use the method on the maybe to recover from a nothing by coalesce calling a function.

When one would like option to a Maybe but would like to remain within a Maybe type, coalesce can be used. coalesce expects (2) Fu Nctions for it ' s inputs.

The first function is used if invoked on a and would Nothing return a Just instance wrapping the result of the function.  The second function is used when coalesce are invoked on a Just and are used to map the original value, returning a new Just Instance wrapping the result of the second function.

The use case of ' coalesce ' was similar to ' Alt ', but instead wrting the function as ' Alt ' does:

 const  getarticlename = obj = Prop ( name   "  // . alt (Maybe.of ( '  

In ' coalesce ', we just combine in one single function:

const Getarticleurl = obj = Prop ('name', obj)    //  If ReturnNothing and then use the first function of coalesce    'page not found', createurlfromname)    . Option ('default'); const URL = getarticleurl (article);

ConstCrocks = require ('crocks')Const{identity, and, compose, IsEmpty, isstring, maybe, not, prop, safe} =crocksConst{Join, split, toLower} = require ('Ramda')ConstArticle ={ID:1, _name:'Learning Crocksjs Functional Programming Library'};ConstCreateurlslug = Compose (Join ('-'), Split (' '), toLower);ConstCreateURL = slug = = ' https://egghead.io/articles/${slug} ';ConstCreateurlfromname =Compose (CreateURL, createurlslug);ConstIsnonemptystring =and (Not (IsEmpty), isstring);ConstGetarticleurl = obj = Prop ('name', obj). Chain (Safe (isnonemptystring))//If return Nothing Then use first function of coalesce. COALESCE (() ='Page not found', createurlfromname). Option ('default');ConstURL =Getarticleurl (article); Console.log (URL)

[Javascript Crocks] Recover from a nothing with the ' coalesce ' Method