Why is std.algorithm so complicated to use?

[Don Clugston]

On 10/07/12 16:59, Andrei Alexandrescu wrote:
> On 7/10/12 9:59 AM, H. S. Teoh wrote:
>> On Tue, Jul 10, 2012 at 09:28:51AM -0400, Andrei Alexandrescu wrote:
>>> On 7/10/12 2:50 AM, Jacob Carlborg wrote:
>>>> On 2012-07-09 22:16, Andrei Alexandrescu wrote:
>>>>
>>>>> So foo is a range of strings, because each element of it is a
>>>>> string.  Then you want to chain a range of strings with a string,
>>>>> which is a range of dchar. That doesn't work, and I agree the error
>>>>> message should be more informative.
>>>>
>>>> Is that by design or something that can be fixed?
>>>
>>> We can arrange things in the library that a custom message is issued,
>>> or in the compiler to do it once for all.
>>
>> Please don't do it in the compiler. Custom messages should be in the
>> library. Tying the compiler to phobos is a bad idea; druntime should be
>> the only dependency.
>
> The idea there being that the compiler could give good details about
> what part of a complex constraint has failed.

However the compiler doesn't know which constraint was supposed to pass.
If it is lucky enough to only have one template, it can do it, but if it 
has:
template1 if (A && B)
template2 if (C && D)
template3 if ( (E || F) && G)

should it print:
foo.d(99): Error: no matching template
foo.d(10):    constraint failed: A
foo.d(28):    constraint failed: D
foo.d(57):    constraint failed: (E || F)
?
Could be a very long list, if there are many templates.

Determining the minimal list of constraints seems like a nice 
application for BDDs...