Parse error on input [GHC-58481]

This is a generic error, indicating that GHC could not parse the code.

GHC contains many more explicit parsing errors with more verbose descriptions of the problem. However if the error is not separately defined there, a problem with parsing is reported with error code GHC-58481.

There may be many different reasons why the error GHC-58481 was emitted, ranging from incorrect syntax that requires additional language extensions, to an expression mistakenly put in the same line as another.

Below are some examples of code that generate this generic parsing error. Please be encouraged to report more or contribute via error-messages github.

Examples

Parse error expression

Error in expression - module keyword should not be used in the same line as an expression declaration.

Error Message

error: [GHC-58481]
    parse error on input ‘module’
  |
5 | foo = 123456                    module
  |                                 ^^^^^^
Example.hs
Before
module Example where


foo = 123456                    module
After
module Example where


foo = 123456
Parse error in OPAQUE pragma

OPAQUE pragma is incorectly parsed.

Error Message

error: [GHC-58481]
    parse error on input ‘[’
  |
4 | {-# OPAQUE[1] f #-}
  |           ^
OpaqueParseFail1.hs
Before
module OpaqueParseFail1 where

f = id
{-# OPAQUE[1] f #-}
After
module OpaqueParseFail1 where

f = id
{-# OPAQUE f #-}
Incorrect syntax of ($) operator usage

When TemplateHaskell is not enabled, then $ denotes function application, but must be followed with a space character: "$ ".

When TemplateHaskell is enabled, $ denotes a splice operator. Used in this context, there must be no space between the “$” and the expression.

Error Message

 warning: [-Woperator-whitespace-ext-conflict] [GHC-47082]
    The prefix use of a ‘$’ would denote an untyped splice
      were the TemplateHaskell extension enabled.
    Suggested fix: Add whitespace after the ‘$’.
  |
3 | f = $(x)
  |     ^

error: [GHC-58481]
    parse error on input ‘$’
    Suggested fix: Perhaps you intended to use TemplateHaskell
  |
3 | f = $(x)
  |     ^
Data.hs
Before
After
{-# LANGUAGE TemplateHaskell #-}
module Data where
import Language.Haskell.TH

x :: Int
x = 42

static :: Q Exp
static = [| x |]

NoHeader.hs
Before
module NoHeader where

f = $(static)
After
{-# LANGUAGE TemplateHaskell #-}
module NoHeader where 
import Data (static)

f = $(static)
Use of pattern synonyms without enabled language extension

In this example the user declared a pattern synonym without enabling the PatternSynonym extension, which leads to this generic parsing error.

messages/GHC-58481/example4/before/Pattern.hs:3:16: error: [GHC-58481]
    parse error on input ‘<-’
    Suggested fix: Possibly caused by a missing 'do'?
  |
3 | pattern Head x <- x:xs
  |                ^^
Pattern.hs
Before

module Pattern where

pattern Head x <- x:xs
After
{-# LANGUAGE PatternSynonyms #-}
module Pattern where

pattern Head x <- x:xs