ghci feature request: partially read modules
Hello. Here is one ghci feature that I find mildly annoying: If ghci (re-)reads a module that contains some error, then it considers the module loading as a complete failure, and at the prompt I get the Prelude environment. I'd like to have at least the import statements executed, and possibly the declarations that were error-free. That would help me in interactively debugging the erraneous part of the module. (Often the error is some type error, related to some imported entity; but when my module contains the error, then the imports are gone.) Perhaps I'm doing something wrong, then please educate me; or perhaps there's an easy way to implement partial reading and typechecking. (It'd be enough to have this for the current module, of course.) Thanks - Johannes Waldmann. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: ghci feature request: partially read modules
On Sat, Feb 16, 2008 at 10:53 AM, Johannes Waldmann [EMAIL PROTECTED] wrote: If ghci (re-)reads a module that contains some error, then it considers the module loading as a complete failure, and at the prompt I get the Prelude environment. I'd like to have at least the import statements executed, and possibly the declarations that were error-free. Seconded. Perhaps I'm doing something wrong, then please educate me; Seconded, again. -- Denis ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: ghci feature request: partially read modules
On Sat, Feb 16, 2008 at 04:53:24PM +0100, Johannes Waldmann wrote:
Hello.
Here is one ghci feature that I find mildly annoying:
If ghci (re-)reads a module that contains some error,
then it considers the module loading as a complete failure,
and at the prompt I get the Prelude environment.
I'd like to have at least the import statements executed,
and possibly the declarations that were error-free.
That would help me in interactively debugging
the erraneous part of the module.
(Often the error is some type error, related to some imported entity;
but when my module contains the error, then the imports are gone.)
Perhaps I'm doing something wrong, then please educate me;
or perhaps there's an easy way to implement partial reading
and typechecking. (It'd be enough to have this for the current
module, of course.)
Thanks - Johannes Waldmann.
This is fairly easy for type errors - just have the 'type of expression'
function return errors using Either etc, and at the top level drop all
expressions with error type.
As for parse errors - good luck. Haskell is incredibly difficult to
parse even if you ignore several of its less-friendly features. If you
allow them... for a long time I said it had never even been proven
possible, but then I found a workable algorithm exponential in the file
size. Now, how do you propose handling parse errors? Here's an example
of why it's hardly trivial:
foo = x + y + z where {
x = 2;
y = 3;
z = 4;
}
Stefan
signature.asc
Description: Digital signature
___
Glasgow-haskell-users mailing list
Glasgow-haskell-users@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: ghci feature request: partially read modules
Sure. Syntax errors are usually easy to spot and fix (for the programmer who uses some reasonable code layout); the motivation for my proposal was type errors. I think it would be perfectly acceptable if ghci rejects modules with parse errors (as it does now) but handles modules with type errors more gracefully. Since type checking a group of declarations (= a module) often considers all declarations at the same time, there may be no sensible way to proceed after a type error. Then it would even be OK to not bind any of the identifiers of the module, as long as the import declarations are available at ghci prompt. (This would still be an improvement over the present situation.) Best regards, Johannes. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
Re: ghci feature request: partially read modules
On Sat, Feb 16, 2008 at 06:58:29PM +0100, Johannes Waldmann wrote: Sure. Syntax errors are usually easy to spot and fix (for the programmer who uses some reasonable code layout); the motivation for my proposal was type errors. I think it would be perfectly acceptable if ghci rejects modules with parse errors (as it does now) but handles modules with type errors more gracefully. Since type checking a group of declarations (= a module) often considers all declarations at the same time, there may be no sensible way to proceed after a type error. Then it would even be OK to not bind any of the identifiers of the module, as long as the import declarations are available at ghci prompt. (This would still be an improvement over the present situation.) Implementing Haskell polymorphism requires that the functions be sorted into dependancy groups, so that undepended definitions can be generalized. Example: foo x = 2 bar = foo 'a' + foo True If this were typechecked all at once (using the standard Damas-Milner algorithm) you would get a cannot match Bool to Char type error. Stefan signature.asc Description: Digital signature ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
