seven-more-languages-in-seven-weeks/slides/factor.org

Seven More Languages in Seven Weeks

Introduction

Introduction

Factor   BMCOL

FACTOR

A stack-based, concatenative programming language

Mr. Miyagi   BMCOL

Day 1

Day 1: Stack On, Stack Off

• Installing Factor
• Using the REPL
• Basic Syntax & Data Types
• Stack Shuffling
• Combinators

Getting Stacked

  "Hello, world" print
  ! Hello, world

  "same" length "diff" length = .
  ! t

Data Types

Booleans

t or f

Sequences

Lists

{ 4 3 2 1 }

Maps

{ { "one" 1 } { "two" 2 } { "three" 3 } }

Quotations

[ 42 + ]

Conditionals

Conditionals take quotations as branching arguments

  10 0 > [ "pos" ] [ "neg" ] if .
  ! pos
  -5 0 > [ "pos" ] [ "neg" ] if .
  ! neg

Stack Shuffling

dup

Duplicate a value on the stack

drop

Drop the top value from the stack

nip

Drop the second value

swap

Swap two values

over

Duplicates the second value over to the top

rot

Rotate the top 3 values on the stack

Combinators

• bi, bi@, bi*
• tri, tri@, tri*
• dip, keep

  44.50 [ 0.05 * ] [ 0.09975 * ] bi
  ! 2.225
  ! 4.438875

  44.50 22.50 [ 0.05 * ] bi@
  ! 2.225
  ! 1.125

  44.50 22.50 [ 0.05 * ] [ 0.09975 * ] bi*
  ! 2.225
  ! 2.244375

Exercises

Exercises

Easy   B_note

Using only * and + , how would you calculate 3^2 + 4^2 with Factor?

  4 dup * 3 dup * + .

Enter USE: math.functions in the Listener. Now, with sq and sqrt , calculate the square root of 3^2 + 4^2 .

  3 sq 4 sq + sqrt .

  1 2
  over swap

  USE: ascii

  "Correl" "Hello, " swap append >upper .

Medium   B_note

Day 2

Day 2: Painting the Fence

• Defining Words
• Vocabularies
• Unit Tests
• Interview with Slava Pestov

Defining Words

  : add-42 ( x -- y ) 42 + ;

  : sum ( seq -- n ) 0 [ + ] reduce ;

  : first-two ( seq -- a b ) [ first ] [ second ] bi ;

Vocabularies

Words are organized into vocabularies, which are similar to packages, modules, or namespaces in other languages.

Unit Tests

Factor includes a unit testing vocabulary (tools.test), which is useful for ensuring correctness of your code, and also experimenting with the language.

  USING: examples.greeter tools.test ;
  IN: examples.greeter.tests

  { "Hello, Test" } [ "Test" greeting ] unit-test

Interview with Slava Pestov

I decided to write my own language, though, because I wanted something really simple, and also just because it would be fun.

Exercises

Exercises

Day 3

Day 3: Balancing on the Boat

• Tuples
• Pipelining with Higher-Order Words

Tuples

1. Defining

     TUPLE: name slot ... ;

2. Accessing and Modifying

   • slot>>
   • >>slot
   • change-slot

3. Creating

   • boa (By Order of Arguments)
   • T{ name { slot value } ... }

Higher-Order Words

  CONSTANT: gst-rate 0.05
  CONSTANT: pst-rate 0.09975

  : gst-pst ( price -- taxes ) [ gst-rate * ] [ pst-rate * ] bi + ;

  : taxes ( checkout taxes-calc -- taxes )
      [ dup base-price>> ] dip
      call >>taxes ; inline

The inline keyword is necessary, as the taxes word takes quotations as parameters.

Wrapping Up

Wrapping Up

Strengths

• Simple syntax
• Easy function composition
• Batteries included

Weaknesses

• Learning curve
• Small community
• Limited resources

Final Thoughts

Final Thoughts