Meeting 19 - Encapsulating Effects

\(\newcommand{\TirName}[1]{\text{#1}} \newcommand{\inferrule}[3][]{ \let\and\qquad \begin{array}{@{}l@{}} \TirName{#1} \\ \displaystyle \frac{#2}{#3} \end{array} } \newcommand{\infer}[3][]{\inferrule[#1]{#2}{#3}} \)

What questions does your neighbor have?

Links

In-Class Slides
In-Class Jupyter
Book Chapter

Announcements

• Lab 4 due Monday Tuesday 6pm
  • Implement static typing (from last Tuesday’s chapter and lecture)
  • Apply higher-order methods for List and Map from HW4
  • For immutable objects and multi-parameter functions, reading semantics
• Lab 4 Leaderboards (Nastiness and Robustness competitions for extra credit).
• Review 3-4 Thursday and Friday
  • Sign up on Canvas – needed to get assignment points
  • Scored on the quality of your feedback for your partner, not how you were assessed by your partner
  • Submit on Gradescope as a group — to get each other’s feedback
  • 0 for no-shows
• Exam 3-4 next Tuesday 11/5
  • 50 minutes in class

Today

• Triage Your Questions
  • Static Type Checking?
  • Higher-Order Functions?
• Encapsulating Effects

Questions?

• Review:
  • What is static type checking and what is the benefit?

Questions?

Error Effects

Exceptions

defined function toDoubleException
res0_1: Double = 1.0
res0_2: Double = 4.2

Option

defined function toDoubleOption

defined function toDoubleNoNaNOption

defined function toDoubleOption
res3_1: Option[Double] = Some(value = 1.0)
res3_2: Option[Double] = Some(value = 4.2)
res3_3: Option[Double] = None

defined function toDoubleNoNaNOption
res4_1: Option[Double] = None
res4_2: Option[Double] = None
res4_3: Option[Double] = None
res4_4: Option[Double] = None

defined function addToDoubleOption
res5_1: Option[Double] = Some(value = 5.2)
res5_2: Option[Double] = None
res5_3: Option[Double] = None

Option as a Collection

defined function toDoubleNoNaNOption

defined function addToDoubleOption

defined function toDoubleNoNaNOption

defined function addToDoubleOption
res9_1: Option[Double] = Some(value = 5.2)
res9_2: Option[Double] = None
res9_3: Option[Double] = None

Map, Filter, FlatMap

Exercise 1 Implement map for Option[A]s:

defined function map

Exercise 2 Implement filter for Option[A]s:

defined function filter

Exercise 3 Implement flatMap for Option[A]s:

defined function flatMap

Comprehensions

defined function addToDoubleOption

defined function addToDoubleOption
res14_1: Option[Double] = Some(value = 5.2)
res14_2: Option[Double] = None
res14_3: Option[Double] = None

Either and Try

defined function toDoubleEither
defined function addToDoubleEither

import scala.util.Try
defined function toDoubleTry
defined function addToDoubleTry

defined function toDoubleEither

import scala.util.Try
defined function toDoubleTry

Mutation Effects

defined function freshVarImperative

defined function freshVar

counter: Int = 3
defined function freshVarImperative
x0: String = "x0"
x1: String = "x1"
x2: String = "x2"

freshVar: Int => (Int, String) = ammonite.$sess.cmd22$Helper$$Lambda$2244/0x0000000800b87840@3d5721bd
counter: Int = 0
counter_: Int = 1
x0: String = "x0"
counter__: Int = 2
x1: String = "x1"
counter___: Int = 3
x2: String = "x2"

counter: Int = 0
x0: String = "x0"
x1: String = "x1"
x2: String = "x2"

Encapsulating Mutation Effects

defined type DoWith

res25: Int => (Int, String) = ammonite.$sess.cmd22$Helper$$Lambda$2244/0x0000000800b87840@3d5721bd

defined function map

defined function flatMap

counter: Int = 0

defined function map

defined function flatMap

counter: Int = 0
counter___: Int = 3
x0: String = "x0"
x1: String = "x1"
x2: String = "x2"

DoWith

defined class DoWith
defined object DoWith
import DoWith._

defined function freshVar

counter: Int = 0

defined function freshVar
res35_1: (Int, String) = (1, "x0")

defined function freshVar
res36_1: (Int, String) = (1, "x0")

counter: Int = 0
counter___: Int = 3
x0: String = "x0"
x1: String = "x1"
x2: String = "x2"

counter: Int = 0
counter___: Int = 3
x0: String = "x0"
x1: String = "x1"
x2: String = "x2"