cgi-3001.1.8.1: A library for writing CGI programs

MaintainerAnders Kaseorg <>




Internal stuff that most people shouldn't have to use. This module mostly deals with the internals of the CGIT monad transformer.


CGI monad class

class Monad m => MonadCGI m whereSource

The class of CGI monads. Most CGI actions can be run in any monad which is an instance of this class, which means that you can use your own monad transformers to add extra functionality.


cgiAddHeader :: HeaderName -> String -> m ()Source

Add a response header.

cgiGet :: (CGIRequest -> a) -> m aSource

Get something from the CGI request.


Monad m => MonadCGI (CGIT m) 

CGI monad transformer

newtype CGIT m a Source

The CGIT monad transformer.



type CGI a = CGIT IO aSource

A simple CGI monad with just IO.

runCGIT :: Monad m => CGIT m a -> CGIRequest -> m (Headers, a)Source

Run a CGI action.

Request info

data CGIRequest Source

The input to a CGI action.




cgiVars :: Map String String

Environment variables.

cgiInputs :: [(String, Input)]

Input parameters. For better laziness in reading inputs, this is not a Map.

cgiRequestBody :: ByteString

Raw request body. To avoid memory leaks, this is the empty string if the request body has been interpreted as inputs in application/x-www-form-urlencoded or multipart/form-data format.


Error handling

throwCGI :: (MonadCGI m, MonadIO m) => SomeException -> m aSource

Throw an exception in a CGI monad. The monad is required to be a MonadIO, so that we can use throwIO to guarantee ordering.

catchCGI :: (MonadCGI m, MonadCatchIO m) => m a -> (SomeException -> m a) -> m aSource

Catches any expection thrown by a CGI action, and uses the given exception handler if an exception is thrown.

tryCGI :: (MonadCGI m, MonadCatchIO m) => m a -> m (Either SomeException a)Source

Catches any exception thrown by an CGI action, and returns either the exception, or if no exception was raised, the result of the action.

handleExceptionCGI :: (MonadCGI m, MonadCatchIO m) => m a -> (SomeException -> m a) -> m aSource

Deprecated version of catchCGI. Use catchCGI instead.