Table of contents

• Table of contents
• fp programming language
• Examples of fp
• Usage
  • Command line
  • Interpret
  • REPL
• Documentation
• Development
  • Nix support
  • Tips
• Credits

fp programming language

fp is a programming language heavily inspired by the language John Backus described in his 1977 Turing Award lecture.

The paper can be found here.

Examples of fp

{- Matrix multiplication.
-}

Def ip ≡ /+∘α*∘⍉

Def mm ≡ α(α ip) ∘ α distl ∘ distr ∘ [~0, ⍉∘~1]

mm:< < <1,2>, <4,5> >,
     < <6,8>, <7,9>> >

Usage

This section will give a quick tour of many of the language features of fp. It will also cover the usage of the tools provided by fp.

Command line

fp can be used without explicitly installing it via nix!

nix run github:japiirainen/fp -- --help
                 
Up to date
Usage: fp COMMAND

  Command-line utility for the `fp` programming language

Available options:
  -h,--help                Show this help text

Available commands:
  interpret                Interpret a `fp` file
  repl                     Enter a REPL for `fp`

Interpret

The interpret command can be used to interpret fp files.

Def ip ≡ /+∘α*∘⍉

ip:<<1,2,3>,<6,5,4>>

This program lives in examples/ip.fp and can be interpreted like this.

cabal run fp -- interpret examples/ip.fp

Which will yield 28.

REPL

you can enter the fp repl to get an interactive environment:

fp repl

λ +:<1,2>
3
λ :let xs = <1,2,3>
λ xs
<1,2,3>

Documentation

Currently the examples directory serves as the documentation! I will list some important topics below for reference.

• Conditionals Fp has a condition expression. It is similar to ternary operator in many ordinary languages.

• While while provides a way to run a specific program many times, specifically until some condition is met.

• Binary to unary bu gives a convenient way to turn binary (2 argument) functions into unary (1 argument) functions. This is kind of like partial application.

• Matrix multiplication This example shows how to do matrix multiplication in fp.

• Factorials A way to compute factorials in fp.

Here's a bunch of primitive functions.

• boolean algebra

• append

• applyToAll

• atom

• const

• construction

• dist

• eq

• id

• length

• nth

• null

• reverse

• transpose

• rotate

• Unbound variable error Fp also has nice error messages.

Development

You can also run the test suite.

cabal test tasty

Nix support

You can alternatively use nix for dev environment and for building the project.

Build:

nix build .

Run:

nix run .

Start Nix shell:

nix-shell

Tips

• Run nix flake update to update all flake inputs.
• Run ./bin/hoogle to start Hoogle with packages in your cabal file.
• Run treefmt in nix shell to autoformat the project. This uses treefmt, which uses ./treefmt.toml (where fourmolu and nixpkgs-fmt are specified).
• Run the application without installing: nix run github:japiirainen/fp (or nix run . from checkout)

fp is a programming language heavily inspired by the language John Backus described in his 1977 Turing Award lecture.

Currently, almost all features described in the paper are implemented. This is not implemented:

• recursion (I'm not sure if I want to allow user defined recursion).

Credits

• Gabriella Gonzalez's (Gabriella439) grace was an invaluable resource for interpreter design in haskell.