Sample run of chapter's interpreter examples
// In file extension-methods/singleSpace-1.scala def singleSpace(s: String): String = s.trim.split("\\s+").mkString(" ")
// In file extension-methods/singleSpace-1.scala singleSpace("A Tale\tof Two Cities") // "A Tale of Two Cities" singleSpace(" It was the\t\tbest\nof times. ") // "It was the best of times."
// In file extension-methods/singleSpace-1.scala val s = "One Fish, Two\tFish " val t = " One Fish, Two Fish" singleSpace(s) == singleSpace(t) // true
s.singleSpace == t.singleSpace // if only this were true
// In file extension-methods/singleSpace-extension.scala extension (s: String) def singleSpace: String = s.trim.split("\\s+").mkString(" ")
// In file extension-methods/singleSpace-extension.scala s.singleSpace == t.singleSpace // It's true!
// In file extension-methods/singleSpace-2.scala // With internal extension marker def singleSpace(s: String): String = s.trim.split("\\s+").mkString(" ")
scala> extension (s: String) | def singleSpace: String = | s.trim.split("\\s+").mkString(" ") def singleSpace(s: String): String
scala> s.singleSpace == t.singleSpace val res0: Boolean = true
// In file extension-methods/generic-extensions-test-1.scala List(1, 2, 3).head // 1 List.empty.head // throws NoSuchElementException
// In file extension-methods/generic-extensions-test-2.scala List(1, 2, 3).headOption // Some(1) List.empty.headOption // None
// In file extension-methods/generic-extensions-test-3.scala List(1, 2, 3).tail // List(2, 3) List.empty.tail // throws NoSuchElementException
// In file extension-methods/tailOption-extension.scala extension [T](xs: List[T]) def tailOption: Option[List[T]] = if xs.nonEmpty then Some(xs.tail) else None
// In file extension-methods/tailOption-extension.scala List(1, 2, 3).tailOption // Some(List(2, 3)) List.empty[Int].tailOption // None List("A", "B", "C").tailOption // Some(List(B, C)) List.empty[String].tailOption // None
// In file extension-methods/tailOption-extension.scala tailOption[Int](List(1, 2, 3)) // Some(List(2, 3))
// In file extension-methods/collective-extensions-1.scala Int.MaxValue // 2147483647 Int.MinValue // -2147483648
// In file extension-methods/collective-extensions-1.scala Int.MinValue.abs // -2147483648 (overflow)
// In file extension-methods/collective-extensions-1.scala extension (n: Int) def absOption: Option[Int] = if n != Int.MinValue then Some(n.abs) else None
// In file extension-methods/collective-extensions-1.scala 42.absOption // Some(42) -42.absOption // Some(42) Int.MaxValue.absOption // Some(2147483647) Int.MinValue.absOption // None
// In file extension-methods/collective-extensions-1.scala -Int.MinValue // -2147483648 (overflow)
// In file extension-methods/int-negateOption.scala extension (n: Int) def absOption: Option[Int] = if n != Int.MinValue then Some(n.abs) else None def negateOption: Option[Int] = if n != Int.MinValue then Some(-n) else None
// In file extension-methods/int-negateOption.scala -42.negateOption // Some(42) 42.negateOption // Some(-42) Int.MaxValue.negateOption // Some(-2147483647) Int.MinValue.negateOption // None
// In file extension-methods/int-extension.scala extension (n: Int) def isMinValue: Boolean = n == Int.MinValue def absOption: Option[Int] = if !isMinValue then Some(n.abs) else None def negateOption: Option[Int] = if !isMinValue then Some(-n) else None
// All with internal extension markers def isMinValue(n: Int): Boolean = n == Int.MinValue def absOption(n: Int): Option[Int] = if !n.isMinValue then Some(n.abs) else None def negateOption(n: Int): Option[Int] = if !n.isMinValue then Some(-n) else None
// In file extension-methods/typeclass-test.scala Long.MinValue.abs // -9223372036854775808 (overflow) -Long.MinValue // -9223372036854775808 (overflow) Short.MinValue.abs // -32768 (overflow) -Short.MinValue // -32768 (overflow) Byte.MinValue.abs // -128 (overflow) -Byte.MinValue // -128 (overflow)
// In file extension-methods/TwosComplement.scala trait TwosComplement[N]: def equalsMinValue(n: N): Boolean def absOf(n: N): N def negationOf(n: N): N object TwosComplement: given tcOfByte: TwosComplement[Byte] with def equalsMinValue(n: Byte) = n == Byte.MinValue def absOf(n: Byte) = n.abs def negationOf(n: Byte) = (-n).toByte given tcOfShort: TwosComplement[Short] with def equalsMinValue(n: Short) = n == Short.MinValue def absOf(n: Short) = n.abs def negationOf(n: Short) = (-n).toShort given tcOfInt: TwosComplement[Int] with def equalsMinValue(n: Int) = n == Int.MinValue def absOf(n: Int) = n.abs def negationOf(n: Int) = -n given tcOfLong: TwosComplement[Long] with def equalsMinValue(n: Long) = n == Long.MinValue def absOf(n: Long) = n.abs def negationOf(n: Long) = -n
// In file extension-methods/TwosComplement-extension.scala extension [N](n: N)(using tc: TwosComplement[N]) def isMinValue: Boolean = tc.equalsMinValue(n) def absOption: Option[N] = if !isMinValue then Some(tc.absOf(n)) else None def negateOption: Option[N] = if !isMinValue then Some(tc.negationOf(n)) else None
// In file extension-methods/TwosComplement-extension.scala Byte.MaxValue.negateOption // Some(-127) Byte.MinValue.negateOption // None Long.MaxValue.negateOption // -9223372036854775807 Long.MinValue.negateOption // None
BigInt(42).negateOption 1 |BigInt(42).negateOption |^^^^^^^^^^^^^^^^^^^^^^^ |value negateOption is not a member of BigInt. |An extension method was tried, but could not be |fully constructed: | | negateOption[BigInt](BigInt.apply(42))( | /* missing */summon[TwosComplement[BigInt]] | )
// In file extension-methods/TwosComplementOps-extension.scala object TwosComplementOps: extension [N](n: N)(using tc: TwosComplement[N]) def isMinValue: Boolean = tc.equalsMinValue(n) def absOption: Option[N] = if !isMinValue then Some(tc.absOf(n)) else None def negateOption: Option[N] = if !isMinValue then Some(tc.negationOf(n)) else None
// In file extension-methods/TwosComplementOps-extension.scala import TwosComplementOps.*
// In file extension-methods/TwosComplementOps-extension.scala -42.absOption // Some(42)
// In file extension-methods/insert.scala def insert[T](x: T, xs: List[T])(using ord: Ord[T]): List[T] = if xs.isEmpty || ord.lteq(x, xs.head) then x :: xs else xs.head :: insert(x, xs.tail)
x <= xs.head // Ah, the clarity!
// In file extension-methods/insert2.scala // (Not yet the best design) object OrdOps: extension [T](lhs: T)(using ord: Ord[T]) def < (rhs: T): Boolean = ord.lt(lhs, rhs) def <= (rhs: T): Boolean = ord.lteq(lhs, rhs) def > (rhs: T): Boolean = ord.gt(lhs, rhs) def >= (rhs: T): Boolean = ord.gteq(lhs, rhs)
// In file extension-methods/insert2.scala def insert[T](x: T, xs: List[T])(using Ord[T]): List[T] = import OrdOps.* if xs.isEmpty || x <= xs.head then x :: xs else xs.head :: insert(x, xs.tail)
// In file extension-methods/insert3.scala trait Ord[T]: def compare(x: T, y: T): Int def lt(x: T, y: T): Boolean = compare(x, y) < 0 def lteq(x: T, y: T): Boolean = compare(x, y) <= 0 def gt(x: T, y: T): Boolean = compare(x, y) > 0 def gteq(x: T, y: T): Boolean = compare(x, y) >= 0 // (This is the best design) extension (lhs: T) def < (rhs: T): Boolean = lt(lhs, rhs) def <= (rhs: T): Boolean = lteq(lhs, rhs) def > (rhs: T): Boolean = gt(lhs, rhs) def >= (rhs: T): Boolean = gteq(lhs, rhs)
// In file extension-methods/insert3.scala def insert[T](x: T, xs: List[T])(using Ord[T]): List[T] = if xs.isEmpty || x <= xs.head then x :: xs else xs.head :: insert(x, xs.tail)
// In file extension-methods/Ord-internal-extension-markers.scala trait Ord[T]: def compare(x: T, y: T): Int def lt(x: T, y: T): Boolean = compare(x, y) < 0 def lteq(x: T, y: T): Boolean = compare(x, y) <= 0 def gt(x: T, y: T): Boolean = compare(x, y) > 0 def gteq(x: T, y: T): Boolean = compare(x, y) >= 0 // With internal extension markers: def < (lhs: T)(rhs: T): Boolean = lt(lhs, rhs) def <= (lhs: T)(rhs: T): Boolean = lteq(lhs, rhs) def > (lhs: T)(rhs: T): Boolean = gt(lhs, rhs) def >= (lhs: T)(rhs: T): Boolean = gteq(lhs, rhs)
// In file extension-methods/TwosComplementOps-absOption-test.scala import TwosComplementOps.absOption 88.absOption // Some(88)
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