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% -----------------------------------------------------------------------------
% $Id: Err.lhs,v 1.1 2001/06/28 14:15:03 simonmar Exp $
%
% (c) The University of Glasgow, 1994-2000
%
\section[GHC.Err]{Module @GHC.Err@}
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.
\begin{code}
{-# OPTIONS -fno-implicit-prelude #-}
module GHC.Err
(
irrefutPatError
, noMethodBindingError
, nonExhaustiveGuardsError
, patError
, recSelError
, recConError
, recUpdError -- :: String -> a
, absentErr, parError -- :: a
, seqError -- :: a
, error -- :: String -> a
, assertError -- :: String -> Bool -> a -> a
, undefined -- :: a
) where
import GHC.Base
import GHC.List ( span )
import GHC.Exception
\end{code}
%*********************************************************
%* *
\subsection{Error-ish functions}
%* *
%*********************************************************
\begin{code}
-- error stops execution and displays an error message
error :: String -> a
error s = throw (ErrorCall s)
-- It is expected that compilers will recognize this and insert error
-- messages which are more appropriate to the context in which undefined
-- appears.
undefined :: a
undefined = error "Prelude.undefined"
\end{code}
%*********************************************************
%* *
\subsection{Compiler generated errors + local utils}
%* *
%*********************************************************
Used for compiler-generated error message;
encoding saves bytes of string junk.
\begin{code}
absentErr, parError, seqError :: a
absentErr = error "Oops! The program has entered an `absent' argument!\n"
parError = error "Oops! Entered GHCerr.parError (a GHC bug -- please report it!)\n"
seqError = error "Oops! Entered seqError (a GHC bug -- please report it!)\n"
\end{code}
\begin{code}
irrefutPatError
, noMethodBindingError
, nonExhaustiveGuardsError
, patError
, recSelError
, recConError
, recUpdError :: String -> a
noMethodBindingError s = throw (NoMethodError (untangle s "No instance nor default method for class operation"))
irrefutPatError s = throw (PatternMatchFail (untangle s "Irrefutable pattern failed for pattern"))
nonExhaustiveGuardsError s = throw (PatternMatchFail (untangle s "Non-exhaustive guards in"))
patError s = throw (PatternMatchFail (untangle s "Non-exhaustive patterns in"))
recSelError s = throw (RecSelError (untangle s "Missing field in record selection"))
recConError s = throw (RecConError (untangle s "Missing field in record construction"))
recUpdError s = throw (RecUpdError (untangle s "Record doesn't contain field(s) to be updated"))
assertError :: String -> Bool -> a -> a
assertError str pred v
| pred = v
| otherwise = throw (AssertionFailed (untangle str "Assertion failed"))
\end{code}
(untangle coded message) expects "coded" to be of the form
"location|details"
It prints
location message details
\begin{code}
untangle :: String -> String -> String
untangle coded message
= location
++ ": "
++ message
++ details
++ "\n"
where
(location, details)
= case (span not_bar coded) of { (loc, rest) ->
case rest of
('|':det) -> (loc, ' ' : det)
_ -> (loc, "")
}
not_bar c = c /= '|'
\end{code}
|
