Towards More Natural Functional Programming Languages

1
Towards MoreNatural Functional Programming
Languages

• Brad A. Myers
• Human-Computer Interaction Institute
• School of Computer Science
• Carnegie Mellon University
• http//www.cs.cmu.edu/bam
• bam_at_cs.cmu.edu

2
The User Interface of Programming Languages

• Programming is a human activity
• Want to improve the ability of people to program
• It makes sense to look at the human side

3

• Millions for compilers but hardly a penny for
  understanding human programming language use.
  Now, programming languages are obviously
  symmetrical, the computer on one side, the
  programmer on the other. In an appropriate
  science of computer languages, one would expect
  that half the effort would be on the computer
  side, understanding how to translate the
  languages into executable form, and half on the
  human side, understanding how to design languages
  that are easy or productive to use.... The human
  and computer parts of programming languages have
  developed in radical asymmetry.

• Allen Newell and Stuart Card, 1985

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What is Usability?

• Usability The effectiveness, efficiency, and
  satisfaction with which users can achieve tasks
  in a particular environment of a product.
• Components
• Learnability Easy to learn so users can get
  started rapidly.
• Effectiveness Experts can use it effectively and
  with high productivity.
• Low Error rate Users make few errors.
• Satisfaction Pleasant to use. No frustrations
  for users.
• Similar to motivations for functional languages

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Why Human Computer Interaction?

• The field of Human Computer Interaction studies
  how to improve and evaluate usability
• Data, knowledge that can guide designs
• To make systems more usable
• Techniques for evaluating usability
• So claims can be substantiated
• So improvements can be made

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Who are the Programmers?
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Design of New Languages

• How make design decisions?
• Based on math, logic, type theory
• Designers intuition or sense of aesthetics
• Similarity to other languages
• But many have known problems
• Key concept
• If you care about usability
• Can leverage off of what is known andwhat can be
  learned about peopleto guide design decisions

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What we are doing...
Studying the People
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Examples of Problems
The men and women here raise your hands!
if ((isMan x) (isWoman x)) then (raise_hands
x) else ()

• (This issue with and applies to other natural
  languages as well.)

( )
( )
if (( not isRed isBlue ) x) then buy x else
()

• Research shows that these differences between
  natural languages and computer languages hurt
  understanding

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My Research Goals

• Make programming significantly easier to learn
  and more effective for non-professional
  programmers and beginners
• Try to provide a more objective basis for
  usability decisions for programming language
  design
• Apply results of Empirical Studies of
  Programmers, Psychology of Programming, and
  Human-Computer Interaction to programming
  language design
• New studies
• Design new programming languages and environments
  based on these results

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Multiple Criteria

• Focusing on learnability and naturalness for
  beginners
• Less emphasis
• Scalability
• Provability
• Efficiency
• Mathematical or Logic properties
• Similarity to other familiar languages
• etc.

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Gentle Slope Systems
DifficultyofUse
Program Complexity and Sophistication
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Gentle Slope Systems
Programming in C
MFC
DifficultyofUse
Program Complexity and Sophistication
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Gentle Slope Systems
Programming in C
FunctionalLanguages?
MFC
UI libraries
DifficultyofUse
Program Complexity and Sophistication
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Gentle Slope Systems
Visual Basic
Programming in C
FunctionalLanguages?
C Programming
MFC
UI libraries
DifficultyofUse
Basic
Program Complexity and Sophistication
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Gentle Slope Systems
Visual Basic
Programming in C
FunctionalLanguages?
C Programming
MFC
UI libraries
DifficultyofUse
Basic
My Goal
Program Complexity and Sophistication
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What is Natural Programming?

• Attempt to make programming closer to the way
  people think
• Make programming more natural
• First, have to find out how people think about
  algorithms, data structures, etc.
• Note Not natural language
• Still creating a formal language

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Why Might Being Natural be Good?

• Programming is the process of transforming a
  mental plan into one that is compatible with the
  computer. Jean-Michel Hoc
• So process might be easier if transformation is
  smaller
• Closeness of mapping
• "The closer the programming world is to the
  problem world, the easier the problem-solving
  ought to be. Conventional textual languages are
  a long way from that goal." Green and Petre

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Why Might Being Natural be Good?

• Example
• Inserting item into 3rd place of high score list
• Conventional Languages
• Loop, starting at end of array, shuffle items
  down, then insert

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Why Might Being Natural be Good?

• Directness (as in Direct Manipulation)
• Distance between one's goals and the actions
  required by the system to achieve those goals.
  Hutchins, Hollan and Norman

vs. VB Let Shape1.FillColor
H00FF00FF ML SetColor ( Shape1, 0x00FF00FF )
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Background Research

• Empirical Studies of Programmers, Psychology of
  Programming, and HCI results not being used in
  the design of new languages
• 30 years of research on what makes languages hard
  to learn and error-prone
• Java / C looping, etc.
• Summarized in our comprehensive tech report
• John Pane and Brad Myers, Usability Issues in
  the Design of Novice Programming Systems TR
  CMU-CS-96-132. Aug, 1996.http//www.cs.cmu.edu/p
  ane/cmu-cs-96-132.html

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Examples of Problems Identified

• Promote Locality and Avoid Hidden Dependencies
• Type definitions often are far from the use
• Code readability is of key importance
• Dont try to reduce keystrokes if makes less
  readable
• Inheritance and object-oriented design are very
  difficult
• Beware of misleading appearances
• When novices and experts mis-read code
• Avoid subtle distinctions in syntax
• E.g., ab vs. ab () vs. vs. gt vs. gt
  vs. -gt

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More Examples

• People expect consistency with external
  representations and usage (math, English, etc.)
• People will search for an analogue in their
  experience that is similar to the syntax
• and aa1 a2 vs. 2a 1ltalt10
• ML is unary negative, - for subtraction 5 -
  2
• So, if different meaning, should have different
  presentation
• Significant difficulties in finding bugs due to
  invisible data, dependencies, and control flow

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HCI Methods for Analyzing Languages

• Analyze languages as user interfaces
• Greens Cognitive Dimensions
• Green and Petre, 1996, Usability Analysis of
  VP Environments A Cognitive Dimensions
  Framework. Journal of VLC, 7(2) 131-174
• 13 dimensions
• Nielsens heuristic analysis principles
• Nielsen, J., Usability Engineering. 1993,
  Boston Academic Press
• 10 principles
• Can also perform usability studies for specific
  issues

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Consistency

• Both a Cognitive Dimension and a Heuristic
  Analysis principle
• C uses the word "static" to mean at least 3
  different things
• In C, can use int a,b to define globals or
  locals, but not as procedure parameters
• Should be able to copy code and use the same code
  elsewhere
• In Visual Basic, to assign something you use
  unless is an object, in which case you use
  Set and "foo 15" vs. "Set foo object
• ML fun f x 0 vs. case e of x gt 0

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Error-Proneness

• HCI Principle Prevent errors
• C and C array bounds errors
• Requiring the "break" in each branch of C, C
  switch statements causes many errors (still in
  Java, fixed in C)
• Small typos can result in compilable programs
  that perform incorrectly, e.g., "" for "
  or"x-3 vs. "x-3 orfun f(SOME _)... (a
  constructor pattern) vs.fun f(SOME_)... (a
  variable)

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Good Error Messages

• Should be clear, helpful, precise, constructive
• Not syntax error
• In C, so much flexibility, compiler often
  doesnt know where error is
• Similar problems with type inference systems
• SML/NJ
• stdIn30.1-30.4 Error operator and operand don't
  agree tycon mismatch
• operator domain ?.t
• operand ?.t
• in expression
• f B

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Closeness of Mapping

• HCI principle Speak the User's Language
• Expressions of algorithms close to the way users
  think of them
• Also, syntactic Issues
• C uses "void" to mean "none", "char" to mean
  8-bit number, ...
• Visual Basic uses "Dim" to declare variables and
  "wend" to end while loops
• Arrays start at 0 whereas people think of
  counting from 1
• Case sensitivity

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Viscosity

• Resistance to local change
• To change parameters of a function in C, have
  to edit .h file and .cpp file, plus all call
  sites
• Changing an if statement into a do statement
  was difficult in early structure editors
• VLs are very difficult due to layout issues
• May have to reposition all lines and boxes to
  make room and neaten resulting drawing
• May need to disconnect and reconnect many wires
• Need for correct indenting may make Haskell
  programs resistant to editing
• But good editor can help

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Less is More

• HCI principle (keep it simple)
• C, C have 16 levels of precedence that have to
  be memorized, some of which are left-associative
  and some are right-associative. Consider
  abcdefgwhich is a legal
  statement in C and C
• Deep nesting in functional languages
• Too many parentheses

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Help the user get started with the system

• Small things should be simple
• Programs that do small things must stilloften be
  very large, e.g., creating awindow containing a
  single red rectangle
• The 2-pages needed in Motif to do Hello World
• zero lines in Visual Basic
• In Java, it still requires
• class HelloWorldApp
• public static void main(String args)
• System.out.println("Hello World!")
• Note 3 kinds of parentheses, 9 special words
• ML print "Hello World!"

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Other Issues

• Many more, seehttp//www.cs.cmu.edu/NatProg/lan
  geval.html
• You can send me examples from each others
  systems!
• But these are mainly good for analysis
• Given a design question, how answer it?

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Our Research

• Lots of gaps in prior research on people and
  programming
• Develop knowledge that can be used in design
• Ph.D. thesis of John Pane
• Available at
• http//www.cs.cmu.edu/pane/thesis/
• Evaluate
• How people express algorithms and think about
  tasks
• Vocabulary and notations used
• Related to the HCI principles of know the user,
  task analysis, and closeness of mapping

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Our Studies so far

• How people naturally express programming concepts
  and algorithms
• 1) Nine scenes from PacMan
• 2) Transforming and calculating data in a
  spreadsheet
• Specific issues of language design
• 3) Selecting specific objects from a group
  (and, or, not)

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Experimental Design

• Question should not bias the answer
• So use pictures instead of textual descriptions
• Concentrate on kids, non-programmers
• Subjects should not be tainted by existing
  programming languages
• Tested that the results generalize to adults and
  programmers

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Study 1

• Usually Pacman moves like this.
• Now let's say we add a wall.
• Pacman moves like this.
• Not like this.

Do this Write a statement that summarizes how I
(as the computer) should move Pacman in relation
to the presence or absence of other things.
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Second Study

• Whether similar results from other domains and
  with adults
• Developed 11 questions with scenarios using
  spreadsheets
• To test database access and operations
• More conventionally computational

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Example Question, 2nd Study
Question 4

• Describe in detailed steps what the computer
  should do tocategorize these people into 2
  groups of Gold and Black.

Firstname
Lastname
Firstname
Lastname

No.



Group

No.



Group



1

Sandra

Bullock


1

Sandra

Bullock

Gold

2

Bill

Clinton


2

Bill

Clinton

Gold

3

Cindy

Crawford

3

Cindy

Crawford


Gold

4

Tom

Cruise


4

Tom

Cruise

Gold

5

Bill

Gates


5

Bill

Gates

Black

6

Whitney

Houston

6

Whitney

Houston


Gold

7

Michael

Jordan


7

Michael

Jordan

Gold

8

Jay

Leno


8

Jay

Leno

Black

9

David

Letterman

9

David

Letterman


Black

10

Will

Smith


10

Will

Smith

Gold
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Results

• Rule-based style If PacMan loses all his lives,
  its game over.
• Some use of Constraint style Pacman cannot go
  through a wall.

• Aggregate operations instead of iterations The
  monsters turn blue and run away Subtract
  20,000 from all elements in Round 2
• These tend to eliminate control structures

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More Results

• The words AND and THEN often used for
  sequencing instead of as a logical operator The
  monsters turn color and start to back up.

• Boolean expression (AND, OR) not common
• Usually had mutually exclusive rulesIf I press
  the up arrow, PacMan goes up. If I press the
  down arrow, PacMan goes down,
• General case first, then exceptions When you
  encounter a ghost, it should kill you. But if
  you get a big pill first you can eat them.

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Yet More Results

• Most arithmetic used natural language styleWhen
  PacMan eats a big dot, the score goes up 100.

• Operations suggest data as lists, not arrays
• People dont make space before inserting
• Objects normally moving If PacMan hits a wall,
  he stops.
• so objects remember their own state
• 2/3 of the first study subjects drew pictures
• Usually to define the initial state

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Third Study Select Objects from a Group

• Concentrate on a known problematic area
• Use of AND, OR, NOT
• Often eliminated from Web searching
• Newsweek reports that less than 6 of users
  manage to use and, or, , -
• Still dominant in all programming languages
• First generate queries given results
• Then, answer queries
• Form-based and Textual formats
• Order was counter-balanced

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Generate Queries
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Answer Queries
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Results

• Using unless did not help accuracyselect the
  objects that are blue unless the objects are
  squarevs.select the objects that match blue
  and not square

• And was a Boolean conjunction sometimesselect
  the objects that match blue and
  circlevs.select the objects that match blue
  and the objects that match circle
• Precedence of not variedselect the objects
  that match not red and square 64 interpreted
  as (not red) and square select the objects
  that match not triangle or green 67
  interpreted as not (triangle or green)

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More results

• 2-D forms helped for generation
• 94 correct with match forms, vs.85 correct
  with text (plt.0001)

(blue and not square) or (circle and not green)
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Implications for New Languages

• For increased usability for novices
• Use event-based style for dynamic events
• Work to minimize the need for control structures
  and variables
• Provide operations on groups of objects
• Data structures that combine the capabilities
  oflists arrays sets
• Support simple arithmetic in natural language
  style (add 1 to score)
• Avoid the use of the word and altogether

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New Language and System HANDS
Human-centered Advances for Novices to Develop
Software

• Video

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Properties of HANDS

• Goal Allow children age 10 to createinteractive
  games and simulations
• Programming in the small (in the tiny)
• Event based computation model
• Metaphor of agent manipulating cards
• All data is visible as properties of the cards
• All operations work on singletons or lists
• No distinction in syntax
• Can generate lists on the fly with queries
• Minimize need for control structures
• Minimize need for local variables

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More Properties of Hands

• Verbose Language
• Easier to read
• No precedence
• Does use parentheses
• But just one kind!
• Environment provide lots of help with syntax and
  graphics
• Tries to be extremely consistent, and also apply
  other HCI rules
• For example, combines IF, CASE (switch), andCOND
  (from Lisp) into one construct

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Conclusions

• Much more research needed on the human side of
  programming
• Usability of languages and environments can be
  improved
• Claims about usability can be tested
• Languages can be evaluated using HCI principles
  and techniques
• If you want a useable and learnable programming
  language, there are data and techniques available
  that can help.

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Credits

• Support for this research has come in part from
  the National Science Foundation underGrant No.
  IRI-9900452
• and
• Grant No. IIS-9817527
• For more information, see
• http//www.cs.cmu.edu/NatProg

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Towards MoreNatural FunctionalProgramming
Languages
Thank You!

• Brad A. Myers
• Human-Computer Interaction Institute
• School of Computer Science
• Carnegie Mellon University
• http//www.cs.cmu.edu/bam
• http//www.cs.cmu.edu/NatProg
• bam_at_cs.cmu.edu