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information. more specifics are given as to the error's nature. e.g. unexpected end or lik.
nameclash etc. If you can recognise certain patterns in an error message. e.g. an unexpected end
of tile has occurred. then a predefined solution could he on hand to he presented to the
programmer.
The afore mentioned unique parts of an error message would form the rules of the expert
system. An example of one of these rules might he :
if "unexpec:.ed end of file" is part of the error message,
appropriate solution for unexpected end of file ......
then offer
The solution that would be presented to the programmer would only form part of the
output. They would also be presented with most of the information that the Miranda compiler
would have originally output. although in a different form. The general format of the output
would be:
A <error t~~e> has been detected on line <line number>
Problem : ~he error itself
Diagnosis
<Solution or hints on how to solve the error>
4.2.1 Function definition errors
Section 3.4.1 highlighted the problem that exists with Function definition errors. in that
you can never be sure that the programmer has implemented a function correctly and specified it
incorrectly or vice versa. All that you can do here is offer some hint as to what the programmer
may wish to do to try and get rid of the error, but never a firm solution. For this reason, Function
definition errors can be considered to be resolvable by inspection.
4.3
Formal parameters and return types
When a Type error occurs in a function, what would constitute a more meaningful error
message than already exists? Let us return to the simple type error:
type error in definition of wrongl
(line 4 of "errors.m") cannot unify bool with num
which is generated when trying to compile the code
> wrongl x = x, if x < 3
= True, otherwise
>
cannot unify num with bool may seem easy enough to understand, and looking
at the code, you can see that the return types are different and have to be altered.
However. the 'new' functional programmer is unlikely to be familiar with the intricacies of
unification and may need some more information on the error that has occurred. General
information about how functions have to return the same types etc. can be provided regardless of
the content of the error message, but to make the information that is provided comprehensive.
some specific information about the function that is in error would need to be given.
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