Specializing on Compile Time Constants

[Jacob Carlborg]

On 10/12/09 23:55, dsimcha wrote:
> == Quote from Jacob Carlborg (doob at me.com)'s article
>> On 10/12/09 23:49, dsimcha wrote:
>>> I'm working on a mathematical expression interpreter for D, which would allow
>>> for closed form mathematical expressions to be specified as string literals at
>>> runtime and be evaluated.  For example:
>>>
>>> MathExp myExpression = mathExp("x^2 + e^cos(-x) - 2 * sqrt(pi)", "x");
>>> writeln(myExpression(2));  // Does exactly what you think it does.
>>>
>>> I've found the syntax so convenient that I'd like to transparently specialize
>>> it on strings known at compile time.  The idea is that, when the expression is
>>> hard-coded, you will still be able to use the MathExp interface, but your
>>> expression will evaluate at the full speed of a statically compiled function.
>>>    Is there any way to test whether the value of an argument to a template
>>> function is known at compile time and specialize on this?
>> Doesn't all values to a template have to be known at compile time
>
> No, I mean the *function* parameters of a template function.

Can't you pass the values as template arguments? Seems you working with 
strings (and numbers?). mathExp!("x^2 + e^cos(-x) - 2 * sqrt(pi)", "x"); 
Note the ! after the function name.