Lua C preprocessor

main.c

/*
 * Copyright (c) 2018 Arvid Gerstmann.
 * This software may be modified and distributed under the terms
 * of the MIT license. See the LICENSE file for details.
 */

#include <stdio.h>

/*lua!
local func = [[

T foo_T(T in) {
    return in;
}

]]

return repl(func, "T", { "int", "float" })
*/

int
main(void)
{
    printf("foo_int: %d\n", foo_int(2));
    printf("foo_float: %f\n", foo_float(1.0f));
    return 0;
}

pre.lua

-- Copyright (c) 2018 Arvid Gerstmann.
-- This software may be modified and distributed under the terms
-- of the MIT license. See the LICENSE file for details.

if #arg == 2 then
    assert(arg[1] ~= arg[2], "arguments must not be the same")
end

local fin = assert(io.open(arg[1], "r"))
local fout = assert(#arg == 2 and io.open(arg[2], "w+") or io.stdout)
local s = fin:read("*all")

local sandbox = {
    debug = print,
    repl = function(code, pattern, repl)
        local out = ""
        for i = 1, #repl do
            out = out .. "\n" .. string.gsub(code, pattern, repl[i])
        end
        return out
    end
}

local out = string.gsub(s, "%/%*lua%!.-\n(.-)%*%/", function(code)
    return assert(load(code, "sandbox", "bt", sandbox))()
end)

fout:write(out)