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Chubek/CurryZoo.lua

Created September 8, 2024 22:53
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The Lua Combinatory Logic Zoo!
Raw
README.md

The Lua script CurryZoo.lua contains a basic 'zoo' of cobinatory logic. It's mainly for demonstration, mind you. There's no entrypoint.

  • S, K and I combinators are the most basic combintors;
  • Functions like 'map' and 'apply', or 'filter', these are 'functors'. The 'map' function is homomorphic with the * operator which is the 'transitive closure operator', but it appears in regular expression as the 'zero or more operator'. A lot is to be said about these.
  • A parsec (parser combintor). zero_or_more is homomorphic (or isomorphic? dunno I'm learning myself) with map.

Enjoy.

Raw
CurryZoo.lua
#!/usr/bin/env lua
function I(x)
return x
end
function K(x, y)
return x
end
function S(fn, gn, x)
return gn(fn(x), gn(x))
end
function map(fn, a)
local result = {}
for x in a do
table.insert(result, fn(x))
end
return result
end
function fold_left(fn, a, init)
local result = init
for i = 1, #a do
result = fn(result, a[i])
end
return result
end
function fold_right(fn, a, init)
local result = init
for i = #a, 0 do
result = fn(result, a[i])
end
return result
end
function apply(fn, a)
local result = a
for i = 1, #a do
result[i] = fn(result[i])
end
return result
end
function filter(fn, a)
local result = {}
for x in a do
if fn(x) then
table.insert(result, x)
end
end
return result
end
function condition(fn, consumer, modifier)
return function()
local x = consumer()
assert(fn(x))
return modifier(x)
end
end
function zero_or_more(parser, modifier)
return function()
local result = {}
while not eof() do
ps = save_parser(parser)
ok, res = pcall(parser)
if not ok then
restore_parser(parser, ps)
break
else
table.insert(result, modifier(res))
end
end
return result
end
end
function one_or_more(parser, modifier)
local rest = zero_or_more(parser)
return function()
return modifier(table.concat(parser(), rest))
end
end
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