F♭ (pronounced F-flat) is a toy language.

F♭ is a dynamically typed array-oriented concatenative language like Forth, Joy, and others. F♭ is meant to be used interactively, for example in a CLI REPL, like R or the command shell, or in a stack based calculator. This constraint dictates many of the language features.

• Designing a programming language in another language is a great way to learn about programming languages in general and the host language in particular.

• Concatenative languages, with inherent functional composition, are a great way to explore functional programming and mathematics. Higher order functions (including math functions) are composed of smaller functions.

• Because 0.1 + 0.2 = 0.3 and sqrt of -1 is not "not a number".

Welcome to F♭ REPL Interpreter F♭ Version 0.0.0 (C) 2000-2017 J. Harshbarger f♭> 0.1 0.2 + [ 0.3 ] f♭> 0.3 = [ true ] f♭> clr [] f♭> -1 sqrt [ 0+1i ] f♭> 1 atan 4 * [ 0+1i, 3.1415926535897932385 ] f♭> * exp [ -1-3.7356616720497115803e-20i ] f♭> abs [ 1 ] f♭> clr [] f♭> "mersenne?" [ 2 swap ^ 1 - prime? ] ; [] f♭> 10 integers [ [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] ] f♭> [ mersenne? ] map [ [ true, true, true, false, true, false, true, false, false, false ] ] f♭> clr [] f♭> 1000 ! [ 4.0238726007709377384e+2567 ] f♭> clr [] f♭> i ! [ 0.49801566811835599106-0.15494982830181068731i ] f♭> { first: "Manfred" } [ { first: 'Manfred' } ] f♭> { last: 'von Thun' } [ { first: 'Manfred' }, { last: 'von Thun' } ] f♭> + [ { first: 'Manfred', last: 'von Thun' } ] f♭> clr [ ] f♭> [ 1 2 3 ] [ [ 1 2 3 ] ] f♭> dup [ [ 1 2 3 ] [ 1 2 3 ] ] f♭> [ 2 * ] [ [ 1 2 3 ] [ 1 2 3 ] [ 2 * ] ] f♭> map [ [ 1 2 3 ] [ 2 4 6 ] ] f♭> + [ [ 1 2 3 2 4 6 ] ] f♭> + [ [ 1 2 3 2 4 6 ] ] f♭> clr [ ] f♭> dbl-sqr-cat: [ dup [ 2 * ] map + ] ; [ ] f♭> [ 1 2 3 ] [ [ 1 2 3 ] ] f♭> dbl-sqr-cat [ [ 1 2 3 2 4 6 ] ] f♭> 'dbl-sqr-cat' see [ '[ dup [ 2 * ] map + ]' ] f♭> drop [ ] f♭> dbl-sqr-cat: expand [ dup,2,*,*,Symbol((),swap,eval,dequote,+ ] 

See other examples and guides here.

• conceptually simple
• interactive first
  • minimal hidden state
  • easy to type and read
  • reads left to right, top to bottom
  • whitespace not significant syntax
  • no lambdas/parameters
  • interactive development
  • case insensitive
• flat concatenative language
  • name code not values
  • multiple return values
  • concatenation is composition/pipeline style
  • no unnecessary parentheses
• no surprises
  • immutable data
  • arbitrary-precision decimal and complex numbers
  • percent values
  • both double and single quotes
  • returns error objects (TBD)
• pure functions
• host language interface (TBD)
• session saving (TBD)
  • undo/redo
  • state is serializable (TBD)
• modules, namespaces, and "closures"

• Many concatenative languages (HP RPL, Forth, Joy, Factor, XY)
• Haskell
• JavaScript

MIT