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no ifs profit
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| /* | |
| * This file has the setup and boilerplate. | |
| * how to calculate the pay for a teacher, and the fee for a student. | |
| * how to find the student or teacher just from a name string, and a | |
| * `List` of names. | |
| */ | |
| type Fee = Double | |
| type Pay = Double | |
| type Balance = Double | |
| sealed trait Person | |
| case class Student(name: String, teacher: Teacher) extends Person | |
| case class Teacher(name: String, students: List[Person]) extends Person | |
| def feeCalc: Student => Fee = _ match { | |
| case Student(_, t) => 1.10 * payCalc(t) / t.students.length | |
| } | |
| def payCalc: Teacher => Pay = _.students.foldLeft(0.0){ | |
| case (pay, t:Teacher) => pay + 0.1 * payCalc(t) | |
| case (pay, s:Student) => pay + 2.5 | |
| } | |
| def feeBalance: Fee => Balance = identity | |
| def payBalance: Pay => Balance = - _ | |
| //Not worrying about the data itself | |
| val names: List[String] = List.empty | |
| def findPerson(name: String): Option[Either[Student, Teacher]] = None |
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| /* | |
| * Lets write down some intermediate helpper functions; | |
| * the information from the signatures (types) of these intermediate functions helps | |
| * document the expected flow | |
| */ | |
| def calc: Either[Student, Teacher] => Either[Fee, Pay] = | |
| feeCalc.choose(payCalc) | |
| def balance: Either[Fee, Pay] => Balance = | |
| feeBalance.choice(payBalance) | |
| def calcBalance: Either[Student, Teacher] => Balance = | |
| calc.andThen(balance) | |
| def nameBalance: String => Option[Balance] = | |
| findPerson(_).map(calcBalance) | |
| // ------------- // | |
| names.foldMap(nameBalance(_).orEmpty) | |
| // res: Balance = 0.0 | |
| // ------------- // | |
| /* this is how it would look like if we avoided the helpers */ | |
| names.foldMap( | |
| findPerson(_).map( | |
| feeCalc.choose(payCalc).andThen(feeBalance.choice(payBalance)) | |
| ).orEmpty | |
| ) | |
| // res: Balance = 0.0 | |
| // ------------- // |
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| /* | |
| * Lets write down some intermediate helpper functions; | |
| * the information from the signatures (types) of these intermediate functions helps | |
| * document the expected flow | |
| */ | |
| def calc: Either[Student, Teacher] => Either[Fee, Pay] = | |
| feeCalc choose payCalc | |
| def balance: Either[Fee, Pay] => Balance = | |
| feeBalance choice payBalance | |
| // ------------- // | |
| names | |
| .flatMap(findPerson) | |
| .map(calc) | |
| .foldMap(balance) | |
| // res: Balance = 0.0 | |
| // ------------- // | |
| /* this is how it would look like if we avoided the helpers */ | |
| names | |
| .flatMap(findPerson) | |
| .map(feeCalc.choose(payCalc)) | |
| .foldMap(feeBalance.choice(payBalance)) | |
| // res: Balance = 0.0 |
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A nice little note is that the merged functions iterates through the array only once, and releases the garbage it generates quicker...