HasCCell

local function URL_encode(str)
   if str then
      str = str:gsub("\n", "\r\n")
      str = str:gsub("([^%w %-%_%.%~])", function(c)
         return ("%%%02X"):format(string.byte(c))
      end)
      str = str:gsub(" ", "+")
   end
   return str
end

local API = "http://tryhaskell.org/eval"

local function evaluate(code, files, stdin)
    local args = json.encode {
        stdin or {},
        files
    }
    local data = string.format("exp=%s&args=%s", URL_encode(code), URL_encode(args))
    local h, err = http.post(API, data, {
        ["User-Agent"] = "HasCCell"
    })
    if err then error(err) end
    local c = h.readAll()
    h.close()
    return json.decode(c)
end

local function save_files(files)
    local f = fs.open(".tryhaskell-files", "w")
    f.write(textutils.serialise(files))
    f.close()
end

local function load_files()
    local f = fs.open(".tryhaskell-files", "r")
    local files = textutils.unserialise(f.readAll())
    f.close()
    return files
end

local function preprocess_output(o)
    local o = o:gsub("‘", "'"):gsub("’", "'")
    return o
end

local history = {}

local files = {}
local ok, result = pcall(load_files)
if ok then files = result end

local last_expr

local function handle_result(result)
    if result.success then
        local s = result.success
        for _, line in pairs(s.stdout) do write(preprocess_output(line)) end
        print(preprocess_output(s.value))
        print("::", preprocess_output(s.type))
        files = s.files
        save_files(files)
    elseif result.error then
        textutils.pagedPrint(preprocess_output(result.error))
    else
        write "-> "
        local next_line = read()
        handle_result(evaluate(last_expr, files, { next_line }))
    end
end

while true do
    write "|> "
    local input = read(nil, history)
    last_expr = input
    table.insert(history, input)
    local result = evaluate(input, files)
    handle_result(result)
end