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README: grammar.

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antirez 2023-02-01 19:14:06 +01:00
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@ -746,7 +746,7 @@ are just list objects, but it is possible to implement Aocla procedures
directly in C. If the `cproc` is not NULL, then it is a C function pointer
implementing a procedure, otherwise the procedure is *user defined*, that menas it is written in Aocla, and we need to evaluate it. We do this with a nested `eval()` call. As you can see, recursion is crucial in writing interpreters.
*A little digression: if we would like to speedup procedure call, we could cache the procedure lookup directly inside the symbol object. However in Aocla procedures can be redefined, so the next time the same procedure name may be bound to a different procedure. To still cache lookedup procedures, a simple way is to use the concept of "epoch". The context has a 64 bit integer called epoch, that is incremented every time a procedure is redefined. So, when we cache the procedure lookup into the object, we also store the current value of the epoch. Then, before using the cached value, we check if the epoch much. If there is no match, we perform the lookup again, and update the cached procedure and the epoch.*
*A little digression: if we would like to speedup procedure call, we could cache the procedure lookup directly inside the symbol object. However in Aocla procedures can be redefined, so the next time the same procedure name may be bound to a different procedure. To still cache lookedup procedures, a simple way is to use the concept of "epoch". The context has a 64 bit integer called epoch, that is incremented every time a procedure is redefined. So, when we cache the procedure lookup into the object, we also store the current value of the epoch. Then, before using the cached value, we check if the epoch maches. If there is no match, we perform the lookup again, and update the cached procedure and the epoch.*
Sorry, let's go back to our `eval` function. Another important thing that's worth noting is that each new Aocla procedure call has its own set of local variables. The scope of local variables, in Aocla, is the lifetime of the procedure call, like in many other languages. So, in the code above, before calling an Aocla procedure we allocate a new stack frame using `newStackFrame()`, then we can finally call `eval()`, free the stack frame and store the old stack frame back in the context structure. Procedures implemented in C don't need a stack frame, as they will not make any use of Aocla local variables. The following is the last part of the `eval()` function implementation: