alicorn 0.1.0

Rust embedding of the Alicorn compiler
Documentation 
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-- SPDX-License-Identifier: Apache-2.0
-- SPDX-FileCopyrightText: 2025 Fundament Software SPC <https://fundament.software>

local lpeg = require "lpeg"

local M = {}

--[[



]]

local function generator_literal(value)
	return function(buff, i)
		buff[i] = value
		return i + 1
	end
end

local function dispatch_tree(buff, i, rules, tree)
	local typ = type(tree)
	if typ == "string" then
		buff[i] = tree
		return i + 1
	elseif typ == "table" then
		if tree.kind then
			if rules[tree.kind] then
				return rules[tree.kind](buff, i, tree)
			else
				error("no rule for the kind " .. tostring(tree.kind))
			end
		else
			error("a tree missing a kind was provided where a kind was required")
		end
	else
		buff[i] = tostring(tree)
		return i + 1
	end
end

local function generator_variable(varname, rules)
	return function(buff, i, data)
		return dispatch_tree(buff, i, rules, data[varname])
	end
end

local function dispatch_treelist(buff, i, rules, sep, tree)
	--print(buff, i, rules, sep, tree)
	local typ = type(tree)
	if typ == "string" then
		buff[i] = tree
		buff[i + 1] = sep
		return i + 2
	elseif typ == "table" then
		if tree.kind then
			if rules[tree.kind] then
				i = rules[tree.kind](buff, i, tree)
				buff[i] = sep
				return i + 1
			else
				error("no rule for the kind " .. tostring(tree.kind))
			end
		else
			if #tree == 0 then
				return i + 1
			end
			for idx, v in ipairs(tree) do
				i = dispatch_treelist(buff, i, rules, sep, v)
			end
			return i
		end
	else
		buff[i] = tostring(tree)
		buff[i + 1] = sep
		return i + 2
	end
end

local function generator_list(sep, varname, rules)
	return function(buff, i, data)
		i = dispatch_treelist(buff, i, rules, sep, data[varname])
		buff[i - 1] = nil
		return i - 1
	end
end

local function generator_compose(a, b)
	return function(buff, i, data)
		return b(buff, a(buff, i, data), data)
	end
end

local compiler_pat
do
	local P, C, Carg, Cf, Cc, Cs = lpeg.P, lpeg.C, lpeg.Carg, lpeg.Cf, lpeg.Cc, lpeg.Cs
	local lc = lpeg.locale()
	local var_pat = (C(lc.alnum ^ 1) * Carg(1)) / generator_variable
	local varlist_pat = (P "(" * C((1 - P ")") ^ 0) * ")" * C(lc.alnum ^ 1) * Carg(1)) / generator_list
	local splice_pat = P "$" * (var_pat + varlist_pat + P "$" * Cc(generator_literal("$")))
	local literal_pat = C((1 - splice_pat) ^ 1) / generator_literal
	compiler_pat = Cf((literal_pat + splice_pat) ^ 0, generator_compose)
end

local generator_mt = {}

function generator_mt:__call(tree)
	local buff = {}
	dispatch_tree(buff, 1, self, tree)
	for k, v in ipairs(buff) do
		--print(k, v)
	end
	return table.concat(buff, "")
end

local function make_generator(desc)
	local self = {}
	for k, v in pairs(desc) do
		self[k] = compiler_pat:match(v, 1, self)
	end
	return setmetatable(self, generator_mt)
end

M.generator = make_generator

return M