functional-programming

问题 I have the classic "Elvis operator" case, where I'm calling methods that each may return null and chaining them together: thing?:nullableMethod1(a)?:nullableMethod2(b)?:nullableMethod3() In Java 8, the most faithful implementation I've found is something like this: return Optional.ofNullable(thing) .flatMap(x -> Optional.ofNullable(x.nullableMethod1(a))) .flatMap(y -> Optional.ofNullable(y.nullableMethod2(b))) .flatMap(z -> Optional.ofNullable(z.nullableMethod3())) I wish that Java's Optional

问题 I have the classic "Elvis operator" case, where I'm calling methods that each may return null and chaining them together: thing?:nullableMethod1(a)?:nullableMethod2(b)?:nullableMethod3() In Java 8, the most faithful implementation I've found is something like this: return Optional.ofNullable(thing) .flatMap(x -> Optional.ofNullable(x.nullableMethod1(a))) .flatMap(y -> Optional.ofNullable(y.nullableMethod2(b))) .flatMap(z -> Optional.ofNullable(z.nullableMethod3())) I wish that Java's Optional

问题 I have the classic "Elvis operator" case, where I'm calling methods that each may return null and chaining them together: thing?:nullableMethod1(a)?:nullableMethod2(b)?:nullableMethod3() In Java 8, the most faithful implementation I've found is something like this: return Optional.ofNullable(thing) .flatMap(x -> Optional.ofNullable(x.nullableMethod1(a))) .flatMap(y -> Optional.ofNullable(y.nullableMethod2(b))) .flatMap(z -> Optional.ofNullable(z.nullableMethod3())) I wish that Java's Optional

问题 I'm new to functional programming and I'm trying rewrite some code to make it more functional-ish to grasp the concepts. Just now I've discovered Array.reduce() function and used it to create an object of arrays of combinations (I've used for loop before that). However, I'm not sure about something. Look at this code: const sortedCombinations = combinations.reduce( (accum, comb) => { if(accum[comb.strength]) { accum[comb.strength].push(comb); } else { accum[comb.strength] = [comb]; } return

问题 This question already has answers here : How to write the dataframes in a list to a single csv file (2 answers) Closed 4 years ago . I'm trying to use the Reduce function in R to use the merge function across multiple dataframes. The problem is, I would like to use the merge function with the argument all=T , and there seems to be nowhere to specify this in the higher-order Reduce function. So I'd like: a <- data.frame(id=c(1, 2, 3, 4), a=c('a', 'b', 'c', 'd')) b <- data.frame(id=c(1, 2, 5, 6

问题 This question already has answers here : How to write the dataframes in a list to a single csv file (2 answers) Closed 4 years ago . I'm trying to use the Reduce function in R to use the merge function across multiple dataframes. The problem is, I would like to use the merge function with the argument all=T , and there seems to be nowhere to specify this in the higher-order Reduce function. So I'd like: a <- data.frame(id=c(1, 2, 3, 4), a=c('a', 'b', 'c', 'd')) b <- data.frame(id=c(1, 2, 5, 6

问题 This question already has answers here : How to write the dataframes in a list to a single csv file (2 answers) Closed 4 years ago . I'm trying to use the Reduce function in R to use the merge function across multiple dataframes. The problem is, I would like to use the merge function with the argument all=T , and there seems to be nowhere to specify this in the higher-order Reduce function. So I'd like: a <- data.frame(id=c(1, 2, 3, 4), a=c('a', 'b', 'c', 'd')) b <- data.frame(id=c(1, 2, 5, 6

问题 I am trying to understand functional programming from first principles, yet I am stuck on the interface between the pure functional world and the impure real world that has state and side effects. From a mathematical perspective, what is a function that returns a function? what is a function that returns an IO action (like Haskell's IO type)? To elaborate: In my understanding, a pure function is a map from domain to co-domain. Ultimately, it is a map from some values in computer memory to

问题 I am trying to understand functional programming from first principles, yet I am stuck on the interface between the pure functional world and the impure real world that has state and side effects. From a mathematical perspective, what is a function that returns a function? what is a function that returns an IO action (like Haskell's IO type)? To elaborate: In my understanding, a pure function is a map from domain to co-domain. Ultimately, it is a map from some values in computer memory to

问题 I am working on scala play framework application. I am trying to call a web service API which takes request payload data as follows { "toID": [ "email1@email.com", "email2@email.com" ], "fromID": "info@test.com", "userID": "ervd12fdsfksdjnfn9832rbjfdsnf", "mailContent": "Dear Sir, ..." } And for this I am using following code ws.url(Utils.messengerServiceUrl + "service/email") .post( Map("userID" -> userID, "mailContent" -> userData.message, "fromID" -> "info@test.com", "toID" -> userData