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Grace An open-source educational programming language Michael Homer - - PowerPoint PPT Presentation

Jun 02, 2023 266 likes •809 views

Grace An open-source educational programming language Michael Homer Why? 2 mwh.nz/LCA2015 Principles Simple programs should be simple Understandable semantic model Support different teaching orders Be a general-purpose language

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SLIDE 1

Grace

An open-source educational programming language Michael Homer

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SLIDE 2

Why?

2 mwh.nz/LCA2015

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SLIDE 3

Principles

  • Simple programs should be simple
  • Understandable semantic model
  • Support different teaching orders
  • Be a general-purpose language

3 mwh.nz/LCA2015

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SLIDE 4

Simple programs should be simple

Incantations package user; class HelloWorld { public static void main(String[] args) { System.out.println("Hello world");

} }

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SLIDE 5

Simple programs should be simple

No Incantations

print "Hello world"

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Understandable semantic model

Method requests people.add(person) print "Hello, world!" // Implicit receiver ((x + y) > z) && !q // Operators are methods

  • bj.x := 2

// Accessor methods 5.between(3)and(8) // Multi-part method name

6 mwh.nz/LCA2015

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SLIDE 7

Understandable semantic model

Control structures if (x < 0) then { print "x is negative"

} else {

print "x is non-negative"

}

while {x > 0} do { x := x − 1

}

7 mwh.nz/LCA2015

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SLIDE 8

Support different teaching orders

Objects and classes

  • bject {

def x is public = 5 var y is public := 7 method distanceTo(other) { ... }

}

class point.x(x’)y(y’) { def x is public = x’ var y is public := y’ method distanceTo(other) { ... }

}

8 mwh.nz/LCA2015

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SLIDE 9

Support different teaching orders

Classes are factories

class point.x(x’)y(y’) { def x is public = x’ var y is public := y’ method distanceTo(other) { ... }

}

means exactly

def point = object { method x(x’)y(y’) {

  • bject {

def x is public = x’ var y is public := y’ method distanceTo(other) { ... }

} } }

9 mwh.nz/LCA2015

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SLIDE 10

Support different teaching orders

Types are optional method sum(a : Number, b : Number) −> Number { return a + b

}

var score : Number := sum(5, 10)

10 mwh.nz/LCA2015

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SLIDE 11

Support different teaching orders

Types are optional method sum(a : Number, b : Number) −> Number { return a + b

}

var score : Number := sum(5, 10) method sum(a, b) { return a + b

}

var score := sum(5, 10)

11 mwh.nz/LCA2015

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SLIDE 12

Tough choices

  • Visibility:

supporting simpler programming or correct engineering?

  • Inheritance: it’s hard.
  • Uniformity or variation?

12 mwh.nz/LCA2015

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Dialects

dialect "beginner" ...

  • A single line to pick one
  • On a per-module basis

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Embracing variation

Standard Grace Engineering Static Dynamic Engineering first Functional Functional objects Static Functional Dynamic Functional Objects Classes Procedural . . . . . . . . . . . . 14 mwh.nz/LCA2015

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Nesting

BeginnerDialect ModuleA ModuleB import "ModuleB"as modb import "ModuleC"as modc import "comp102"as c102 TypedDialect ModuleC StandardGrace comp102

15 mwh.nz/LCA2015

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My favourite Java error

1 class Counter { 2 int total = 0; 3 int add(int n) { 4 return ( total += n); 5

}

6 int addAllNegative(Iterable<Integer> all) { 7 for (int n : all ) 8 if (n < 0) 9 int tot = add(−n); 10 return total ; 11

}

12 }

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My favourite Java error

1 class Counter { 2 int total = 0; 3 int add(int n) { 4 return ( total += n); 5

}

6 int addAllNegative(Iterable<Integer> all) { 7 for (int n : all ) 8 if (n < 0) 9 int tot = add(−n); 10 return total ; 11

}

12 } Counter.java:9: error: ’.class’ expected int tot = add(-n); ˆ

17 mwh.nz/LCA2015

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Pattern matching

match(x) // x : 0 | String | Student // Match against a literal case { 0 −> print "Zero" } // Typematch, binding a variable case { s : String −> print(s) } // Destructuring match case { : Student(name, id)−> print(name)}

18 mwh.nz/LCA2015

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Pattern matching

match(x) // x : 0 | String | Student // Match against a literal case { 0 −> print "Zero" } // Typematch, binding a variable case { s : String −> print(s) } // Destructuring match case { : Student(name, id)−> print(name)}

19 mwh.nz/LCA2015

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Pattern matching

match(x) // Nested patterns case { p : Point(0,y) −> print "(0,{y})" } // Pattern operators case { p : Point(0, ) | Point3D(0, , )

−> print(p) }

case { s : Seq & Dog

−> s.bark(s.size)}

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Extensible patterns

if (Point.match(x)) then { ...

}

method match(o : Any)

−> SuccessfulMatch | FailedMatch { ... }

21 mwh.nz/LCA2015

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Implementation

Minigrace

  • Written in Grace
  • Supports everything here, targets C and JavaScript

Compiler source code (in Grace): github/mwh/minigrace Tarballs (pregenerated C code): ecs.vuw.ac.nz/∼mwh/minigrace/ Client-side web front-end: ecs.vuw.ac.nz/∼mwh/minigrace/js

Hopper

  • Written in concurrent JavaScript: github/zmthy/hopper
  • Had its own talk on Wednesday

All links, and more, available from 22 mwh.nz/LCA2015

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SLIDE 23

Live demo

!

23 mwh.nz/LCA2015

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Tiled Grace experiment

  • 33 participants, mostly students
  • 5 tasks, fully instrumented
2 4 6 5 10 15 20 Total number of switches of view count

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SLIDE 25

Grace

An open-source educational programming language Michael Homer

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SLIDE 26

26 mwh.nz/LCA2015

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Additional slides

Extra details that may be helpful 27 mwh.nz/LCA2015

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Loop invariants

Module “loopinvariant”: method for(it : Iterable ) invariant (inv : Block<Boolean>)do(blk : Block) { for ( it ) do {i−> if (! inv.apply) then { InvariantFailure .raise "Loop invariant not satisfied."

}

blk.apply(i )

}

if (! inv.apply) then { InvariantFailure .raise "Loop invariant not satisfied."

} }

28 mwh.nz/LCA2015

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Loop invariants client code

dialect "loopinvariant" var sum : Number := 0 for (1..10) invariant { sum > 0 } do { item : Number −> sum := sum + item

}

http://ecs.vuw.ac.nz/˜mwh/minigrace/js/#sample= loopinvariant_example 29 mwh.nz/LCA2015

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Pluggable checkers

import "StandardPrelude" as StandardPrelude inherits StandardPrelude.new def CheckerFailure = Exception.refine "CheckerFailure" method checker(nodes) { for (nodes) do {n−> if (n.kind == "vardec") then { CheckerFailure.raiseWith("var declarations are not allowed at the top level", n. name)

} } }

30 mwh.nz/LCA2015

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Dialect-support dialect

dialect "dialect" import "StandardPrelude" as StandardPrelude inherits StandardPrelude.new fail "var declarations not allowed" when { v : VarDec −> true } method checker(l) { check(l)

}

Similar: http://ecs.vuw.ac.nz/˜mwh/minigrace/js/ #sample=dialect_example 31 mwh.nz/LCA2015

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DSLs: Object associations

dialect "object-associations" def Attends = Relationship<Student, Course> def Teaches = Relationship<Course, Faculty> def Prerequisites = ReflexiveRelationship<Course> // Set up or obtain our data objects def james = student (...) ... Attends.add(james, cs102) ... for (Attends.to(cs102)) do { each −> ... }

http://ecs.vuw.ac.nz/˜mwh/minigrace/js/#sample= ObjectAssociations_example 32 mwh.nz/LCA2015

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DSLs: Finite State Machines

dialect "fsm" def startState = state { print "Starting" } def runState = state { print "Running" } def endState = state { print "Done" } in(startState) on("A") goto(runState) in(runState)

  • n("A") goto(runState)
  • n("B") goto(endState)

method process(symbol : String) { transition (symbol)

}

http://ecs.vuw.ac.nz/˜mwh/minigrace/js/#sample=fsm_ example 33 mwh.nz/LCA2015

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SLIDE 34

The extreme: GrAPL

dialect "grapl" N ← [1, 2, 3, 4] print (N) print (N + 2) print (+/N) // Standard Lotto example print (L[ |

(L ← (n 6 ? 40))])

// Calculate primes up to 20 - note that the / // function has its parameters reversed here, // because of Grace’s evaluation order. print ((P ← (n 1 ι 20))/ ∼(P∈(P◦·∗P)))

http://ecs.vuw.ac.nz/˜mwh/minigrace/js/#sample= grapl_example 34 mwh.nz/LCA2015

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SLIDE 35

What is pattern-matching?

Take an object. Do “something” if it’s an object the pattern matches. Otherwise, try the next pattern or error.

35 mwh.nz/LCA2015

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What does pattern-matching mean?

Take an object. Do “something” if it’s an object the pattern matches. Otherwise, try the next pattern or error. Pattern-matching is applying a partial function.

f(x) = −x when x < 0 f(x) = x

  • therwise

36 mwh.nz/LCA2015

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Match results

if (Point.match(x)) then { ...

}

def matchResult = Point.match(x) def values : Tuple<Number, Number> = matchResult.bindings def p : Point = matchResult.result

37 mwh.nz/LCA2015

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Exceptions

  • Want a hierarchy of errors. . .
  • . . . but they all have the same type.
  • Pattern-matching!

38 mwh.nz/LCA2015

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Exceptions as patterns

def MyError = Error.refine "MyError" def NegativeError = MyError.refine " NegativeError" try { if (value < 0) then { NegativeError.raise "{value} < 0"

} } catch {e : MyError −> print "Error: {e}" }

39 mwh.nz/LCA2015

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Blocks Are objects:

def welcome = { n−> print "Hello {n}" } welcome.apply "World"

  • bject { // Almost:

method apply(n) { print "Hello {n}"

} // In fact, self } // is unchanged

40 mwh.nz/LCA2015

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Experiment

  • Anonymised data set available
  • Includes instrumentation and analysis tooling
  • Complete (52-page) writeup of protocol and

results also available

  • All of this accessible from mwh.nz/LCA2015

41 mwh.nz/LCA2015

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Fun by experience

0% 10% 20% 30% 40% 1 Agree 2 3 4 Neutral 5 6 7 Disagree

The system was fun to use Percentage choosing each option

How many technologies used Ten or fewer More than ten

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Freeform likes

Appearance Colour Errors Overview Revert Switching Syntax Toolbox Var list 3 6 9 count What did you like about this system? (coded)

43 mwh.nz/LCA2015

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Freeform dislikes

Button placement Change op Dataflow unclear Dislike GUIs Drag from middle Dragging hard Multiple runs New language No default in holes No switch with error Unfamiliar 0.0 2.5 5.0 7.5 10.0 count What did you dislike about this system? (coded)

44 mwh.nz/LCA2015

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Type operations

  • Variants: Point | Nil

x : A | B ≡ x : A ∨ x : B def nilValue : Nil = ... var p : Point | Nil := nilValue // OK ... p := CartesianPoint.new(3,4) // OK

  • Intersubsection: T1 & T2 conforms to T1 and

T2

45 mwh.nz/LCA2015

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Gradual types and inheritance

class x.new { method a { self.b

} }

class y.new { inherits x.new method b { print "B" }

}

y.new.a

46 mwh.nz/LCA2015

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Contents

Title slide 1 Why now? 2 Principles 3 Simple programs should be simple 4 Incantations . . . . . . . . . . . . . . . . . . . . . . . . . 4 Incantations . . . . . . . . . . . . . . . . . . . . . . . 5 47 mwh.nz/LCA2015

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SLIDE 48

Understandable semantic model 6 Method requests . . . . . . . . . . . . . . . . . . . . . . . 6 Control structures . . . . . . . . . . . . . . . . . . . . . . 7 Support different teaching orders 8 Objects and classes . . . . . . . . . . . . . . . . . . . . . 8 Classes are factories . . . . . . . . . . . . . . . . . . 9 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Types are optional . . . . . . . . . . . . . . . . . . . . 11 48 mwh.nz/LCA2015

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Tough choices 12 Dialects 13 Embracing variation . . . . . . . . . . . . . . . . . . . . . 14 Nesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 My favourite Java error . . . . . . . . . . . . . . . . . . . . 16 The message . . . . . . . . . . . . . . . . . . . . . . 17 Pattern matching 18 A digression . . . . . . . . . . . . . . . . . . . . . . . . . 19 Pattern matching redux . . . . . . . . . . . . . . . . . . . . 20 Extensible patterns . . . . . . . . . . . . . . . . . . . . . . 21 49 mwh.nz/LCA2015

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Implementation 22 Live demo 23 Tiled Grace experiment 24 Ending slide 25 Reminder 26 50 mwh.nz/LCA2015

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Additional slides 27 Dialect samples . . . . . . . . . . . . . . . . . . . . . . . 28 Loop invariants . . . . . . . . . . . . . . . . . . . . . 28 Loop invariants client code . . . . . . . . . . . . . . . 29 Pluggable checkers . . . . . . . . . . . . . . . . . . . 30 Dialect-support dialect . . . . . . . . . . . . . . . . . 31 DSLs: Object associations . . . . . . . . . . . . . . . 32 DSLs: Finite State Machines . . . . . . . . . . . . . . 33 The extreme: GrAPL . . . . . . . . . . . . . . . . . . 34 51 mwh.nz/LCA2015

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What is pattern-matching? . . . . . . . . . . . . . . . . . . 35 Partial functions . . . . . . . . . . . . . . . . . . . . . 36 Match results . . . . . . . . . . . . . . . . . . . . . . . . . 37 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Exceptions as patterns . . . . . . . . . . . . . . . . . 39 Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Fun by experience . . . . . . . . . . . . . . . . . . . 42 Freeform likes . . . . . . . . . . . . . . . . . . . . . . 43 Freeform dislikes . . . . . . . . . . . . . . . . . . . . 44 Type operations . . . . . . . . . . . . . . . . . . . . . . . 45 Gradual types and inheritance . . . . . . . . . . . . . . . . 46 52 mwh.nz/LCA2015

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Contents 47 53 mwh.nz/LCA2015