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{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE NoImplicitPrelude, MagicHash, ImplicitParams #-}
{-# LANGUAGE RankNTypes, TypeInType #-}
{-# OPTIONS_HADDOCK hide #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Err
-- Copyright : (c) The University of Glasgow, 1994-2002
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC extensions)
--
-- The "GHC.Err" module defines the code for the wired-in error functions,
-- which have a special type in the compiler (with \"open tyvars\").
--
-- We cannot define these functions in a module where they might be used
-- (e.g., "GHC.Base"), because the magical wired-in type will get confused
-- with what the typechecker figures out.
--
-----------------------------------------------------------------------------
module GHC.Err( absentErr, error, errorWithoutStackTrace, undefined ) where
import GHC.CString ()
import GHC.Types (Char, RuntimeRep, TYPE)
import GHC.Stack.Types
import GHC.Prim
import GHC.Integer () -- Make sure Integer is compiled first
-- because GHC depends on it in a wired-in way
-- so the build system doesn't see the dependency
import {-# SOURCE #-} GHC.Exception( errorCallWithCallStackException )
-- | 'error' stops execution and displays an error message.
error :: forall (r :: RuntimeRep). forall (a :: TYPE r).
HasCallStack => [Char] -> a
error s = raise# (errorCallWithCallStackException s ?callStack)
-- Bleh, we should be using 'GHC.Stack.callStack' instead of
-- '?callStack' here, but 'GHC.Stack.callStack' depends on
-- 'GHC.Stack.popCallStack', which is partial and depends on
-- 'error'.. Do as I say, not as I do.
-- | A variant of 'error' that does not produce a stack trace.
--
-- @since 4.9.0.0
errorWithoutStackTrace :: forall (r :: RuntimeRep). forall (a :: TYPE r).
[Char] -> a
errorWithoutStackTrace s =
-- we don't have withFrozenCallStack yet, so we just inline the definition
let ?callStack = freezeCallStack emptyCallStack
in error s
-- Note [Errors in base]
-- ~~~~~~~~~~~~~~~~~~~~~
-- As of base-4.9.0.0, `error` produces a stack trace alongside the
-- error message using the HasCallStack machinery. This provides
-- a partial stack trace, containing the call-site of each function
-- with a HasCallStack constraint.
--
-- In base, however, the only functions that have such constraints are
-- error and undefined, so the stack traces from partial functions in
-- base will never contain a call-site in user code. Instead we'll
-- usually just get the actual call to error. Base functions already
-- have a good habit of providing detailed error messages, including the
-- name of the offending partial function, so the partial stack-trace
-- does not provide any extra information, just noise. Thus, we export
-- the callstack-aware error, but within base we use the
-- errorWithoutStackTrace variant for more hygienic error messages.
-- | A special case of 'error'.
-- It is expected that compilers will recognize this and insert error
-- messages which are more appropriate to the context in which 'undefined'
-- appears.
undefined :: forall (r :: RuntimeRep). forall (a :: TYPE r).
HasCallStack => a
undefined = error "Prelude.undefined"
-- | Used for compiler-generated error message;
-- encoding saves bytes of string junk.
absentErr :: a
absentErr = errorWithoutStackTrace "Oops! The program has entered an `absent' argument!\n"
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