[racket-dev] error-message overhaul

New error format: +2
Changing my code: -1

Overall, +1. :D  Should we have a Big Push to convert error message call 
sites, starting with actively maintained code?

Neil ⊥

On 05/26/2012 06:09 AM, Matthew Flatt wrote:
> I've pushed a first cut at overhauling error messages from `racket/base'.
>
> The old error message convention tried to keep everything on one line,
> but that sometimes got long and contorted. The old format didn't work
> at all for contract errors, for example, and so I've more or less
> adopted the contract-error style everywhere.
>
> The new error message convention encourages a short message on the
> first line, and then more information in separate "<field>:<detail>"
> lines. A multi-line<detail>  starts out on its old line and is indented
> by an extra space. Where the old format would inline a value or name in
> the message, the new format puts the value or name in its own field or
> line. A source locations is similarly moved to a field, instead of
> prefixing the error message. Finally, instead of a separate " ===
> context ===" section for a backtrace, it's added by the default
> exception printer as a "context" field.
>
> There's a new `raise-argument-error' function to replace existing uses
> of `raise-type-error'. For example
>
>    (raise-type-error 'eat "integer" n)
>
> should change to
>
>    (raise-argument-error 'eat "integer?" n)
>
> A new `raise-arguments-error' (plural) function supports simple error
> messages that have any number of fields, where each field's value is
> `print'ed into the message:
>
>    (raise-arguments-error 'eat
>                           "fish is smaller than its given meal"
>                           "fish size" 12
>                           "given meal size" 13)
>
> There's more room for error-formatting support, and I have some ideas
> --- but also I have plenty still to do for just with the the simple
> ones.
>
> The old error-message functions remain and format messages as before
> (although, notably, `raise-syntax-error' uses the new conventions).
> Conversion to the new format mostly requires changing all existing call
> sites.
>
> You may wonder whether exception records should provide field and
> detail information directly, instead of only encoded in the
> error-message string. As appealing as that sounds, retrofitting
> existing code to use a new little DSL for error content looks to me
> like far too much work. I have some ideas on how to get much of the
> benefit indirectly, though (so that DrRacket can show images when they
> appear in an error, for example, instead of printing "#<image>"). For
> now, if you convert error messages to `raise-argument-error' and
> `raise-arguments-error', then you're certainly future-proof for that
> step. Even if you build messages by hand, I expect that format strings
> will work transparently. More soon...
>
>
> Some examples:
>
> ----------------------------------------
>> (+ 1 'a)
> +: contract violation
>    expected: number?
>    given: 'a
>    argument position: 2nd
>    other arguments:
>      1
>    context:
>     /Users/mflatt/proj/plt/collects/racket/private/misc.rkt:87:7
>> (add1)
> application: wrong number of arguments
>    procedure: add1
>    expected number of arguments: 1
>    given number of arguments: 0
>    context:
>     /Users/mflatt/proj/plt/collects/racket/private/misc.rkt:87:7
>> (lambda x)
> lambda: bad syntax
>    in: (lambda x)
>    source:
>     readline-input::16
>    context:
>     /Users/mflatt/proj/plt/collects/racket/private/misc.rkt:87:7
>> .
> read: illegal use of "."
>    source:
>     readline-input::27
>    context:
>     /Users/mflatt/proj/plt/collects/readline/pread.rkt:230:0: read-cmdline-syntax
>     /Users/mflatt/proj/plt/collects/racket/private/misc.rkt:87:7
>> (collection-path "nonesuch")
> collection-path: collection not found
>    collection: "nonesuch"
>    in collection directories:
>     /Users/mflatt/Library/Racket/5.3.0.9/collects
>     /Users/mflatt/proj/plt/collects
>    context:
>     /Users/mflatt/proj/plt/collects/racket/private/pre-base.rkt:111:53: fail
>     /Users/mflatt/proj/plt/collects/racket/private/misc.rkt:87:7
> ----------------------------------------
>
> For comparison, here are the same examples with the old message style:
>
> ----------------------------------------
>> (+ 1 'a)
> +: expects type<number>  as 2nd argument, given: 'a; other arguments were: 1
>
>   === context ===
> /Applications/Racket v5.2.1/collects/racket/private/misc.rkt:87:7
>
>> (add1)
> add1: expects 1 argument, given 0
>
>   === context ===
> /Applications/Racket v5.2.1/collects/racket/private/misc.rkt:87:7
>
>> (lambda x)
> readline-input::16: lambda: bad syntax in: (lambda x)
>
>   === context ===
> /Applications/Racket v5.2.1/collects/racket/private/misc.rkt:87:7
>
>> .
> readline-input::27: read: illegal use of "."
>
>   === context ===
> /Applications/Racket v5.2.1/collects/readline/pread.rkt:230:0: read-cmdline-syntax
> /Applications/Racket v5.2.1/collects/racket/private/misc.rkt:87:7
>
>> (collection-path "nonesuch")
> collection-path: collection not found: "nonesuch" in any of: (#<path:/Users/mflatt/Library/Racket/5.2.1/collects>  #<path:/Applications/Racket v5.2.1/collects>)
>
>   === context ===
> /Applications/Racket v5.2.1/collects/racket/private/pre-base.rkt:111:53: fail
> /Applications/Racket v5.2.1/collects/racket/private/misc.rkt:87:7
>
> ----------------------------------------
>
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