Pirogue is a concatenative language built to explore concatenative combinators and other ideas outlined here. It's inspired by Joy, Forth, and Stck.
A Cajun Pirogue is a small, flat bottomed boat built for the shallow marshes and bayous in Louisiana. It's said that a pirogue can "can float on a heavy dew".
With rust installed:
cargo run --release
The syntax is just a flat series of tokens. There are only 3 datatypes: ints, symbols, and quotes.
For example to add two numbers, push both onto the stack then use the builtin + symbol to add them.
>> 1 2 +
[3]
If a symbol is not defined, it will just be pushed onto the top of the stack like any other value:
>> 1 a 2 b
[1 a 2 b]
A quote is any valid program and can be pushed onto the stack. You enclose in [ ] to denote a quote:
>> [1 2 +]
[[1 2 +]]
You can think of a quote like an anonymous function. It can be "evaluated" with i:
>> [1 2 +] i
[3]
With this, you can define new functions with the define function. It expects a quote (the function body) and a symbol (the function name) on top of the stack:
>> [1 +] add1 define
[]
>> 41 add1
[42]
With these primitives you can do a lot, but in order to create higher level functions and syntax we provide some combinators and stack manipulation functions:
swap, zap, and dup, and over are all familiar to languages like forth:
>> a b
[a b]
>> swap
[b a]
>> swap
[a b]
>> dup
[a b b]
>> zap
[a b]
>> over
[a b a]
There are some functions that operate on the top 3 elements, like the classic rot:
>> a b c
[a b c]
>> rot
[b c a]
>> rot
[c a b]
>> rot
[a b c]
There are also some functions that operate on quotes allowing you to write programs that manipulate other programs. You can learn more about these in this article about concatenative combinators in Joy.
dip expects two quotes on the stack, it evals the top and swaps the order:
>> [b] [a]
[[b] [a]]
>> dip
[a [b]]
unit is sort of the inverse of i in that it wraps the quote in a quote:
>> [a]
[[a]]
>> unit
[[[a]]]
>> unit
[[[[a]]]]
>> i
[[[a]]]
>> i
[[a]]
cat allows you to concatentate two quotes:
>> [b] [a] cat
[[b a]]
cons can do the same but leaves the bottom element quoted:
>> [b] [a] cons
[[[b] a]]