FP15

FP15 is a strict, dynamically-typed function-level programming language based on the FP programming language created by John Backus.

Some major departures from the original FP are (1) left-to-right reading, (2) no explicit constant function and (3) user-defined functionals.

Introduction

In function-level programming (also called point-free and tacit), functions are defined without mentioning any of their arguments.

Here is the factorial function in FP15:

fac = (=0) : 1 | (* (-1) fac)

Here is a function that finds Pythagorean triples upto a number:

pytr = [(1..), (1..), (1..2*)] cross ?(#0^2 + #1^2 = #2^2)

Example:

> 15 pytr
[[3, 4, 5], [4, 3, 5], [5, 12, 13], [6, 8, 10], [8, 6, 10],
 [8, 15, 17], [9, 12, 15], [12, 5, 13], [12, 9, 15], [15, 8, 17]]

Setup

You can provision the Vagrant machine.

# Build
cabal sandbox init
cabal install --only-dependencies
cabal configure
cabal build

# Run REPL
./fp15-repl.py

# Run a file (using the main function)
cabal run < example.fp

Tutorial

See Tutorial.md.

Task List

Language Features

• Empty list items
• Smart spitting
• Infix notation
• Comma notation
• Unicode escapes in string literals
• User-defined operator definitions
• User-defined ternary operator support
• Recursive block
• Local definitions
• User-defined functionals

Runtime

• Embed multiple compilation phases within Expr
• Context stack
• I/O support
• Reference cells and arrays
• Actual higher-order functions
• Uniqueness typing enforcement

Code

• Refactor name resolution so absolute and relative names are distinguhshed