JuliaFunctional / Monadic.jl

simple macro for monadic programming style

Monadic

This package provides the macro @monadic and its little helper @pure.

With both you can define custom monadic syntax, let's look at an example to clarifiy what this means.

my_map(f, a::Vector) = f.(a)
my_flatmap(f, a::Vector) = vcat(f.(a)...)
# to show you what flatmap does, a small example
my_flatmap(x -> [x, x], [1, 2])  # [1, 1, 2, 2]  i.e. it applies `f` to every element and concatenates all results

using Monadic
@monadic my_map my_flatmap begin
  a = [:a,:b]
  b = [1, 2]
  c = [b + 4, b + 5]
  @pure Symbol(a, b, c)
end
# returns [:a15, :a16, :a26, :a27, :b15, :b16, :b26, :b27]

Apparently, this use of @monadic works like a nested for-loop, collecting the results.

To summarize what happens is that each line is interpreted as a kind of context or context-assignment (instead of a usual value or value assignment in normal syntax). With the @pure macro you can indicate that the code should be interpreted normally (without context).

The context here is defined by our Vector, which we interpreted by my_map and my_flatmap as a kind of "do the computation for all combinations". It is like a context for indeterminism.

So let's read the @monadic syntax out loud:

for every a in [:a, :b]
for every b in [1, 2]
for every c in [b + 4, b + 5]
do a normal computation `Symbol(a, b, c)` (because it is prepended with `@pure`)
and collect the last computation for all combinations (because it is the last expression)

For more details check out the documentation.

Installation

To install the package, use the following command inside the Julia REPL:

using Pkg
pkg"add Monadic"

To load the package, use the command:

using Monadic

It will give you the macros @monadic and @pure.