[yorwba]

Apparently the solution is to check the type before you declare it: https://stackoverflow.com/questions/32321054/using-declare-t...

I assume that most CL compilers are smart enough to optimize calls to such checking functions when they occur in a context where the type has already been declared. And you can probably write a macro to make it more convenient ...

[dreamcompiler]

There's no guarantee any given CL compiler will optimize such calls away. It would probably be considered wrong for the compiler to optimize them away. Remember that type declarations mean "don't check the type, ever." They do not mean "check the type at compile time" because CL never checks types at compile time.[1]

The technique in the example can defeat the purpose in simple cases (like the example) because type declarations removed runtime type checking and then you manually added it back in.

But it's a useful technique in cases such as an inner loop from which you remove type checking inside the loop, but move it out of the loop. This is an advanced CL technique. You have to be very careful about such things as adding 1 to a fixnum in the loop and possibly overflowing it, which is exactly what you have to care about in C.

[1] modulo certain compiler quirks and the use of compiler macros, which are an advanced technique.

[lispm]

> CL never checks types at compile time

SBCL, CMUCL, Scieneer CL do.

http://www.sbcl.org/manual/#Declarations-as-Assertions