With the exceptions listed below, clauses are executed in the loop body in the order in which they appear in the source. Execution is repeated until a clause terminates the loop or until a return, go, or throw form is encountered which transfers control to a point outside of the loop. The following actions are exceptions to the linear order of execution:
All variables are initialized first, regardless of where the establishing clauses appear in the source. The order of initialization follows the order of these clauses.
The code for any initially clauses is collected
into one progn in the order in which the clauses appear in
the source. The collected code is executed once in the loop prologue
after any implicit variable initializations.
The code for any finally clauses is collected
into one progn in the order in which the clauses appear in
the source. The collected code is executed once in the loop epilogue
before any implicit values from the accumulation clauses are returned.
Explicit returns anywhere in the source, however, will exit the
loop without executing the epilogue code.
A with clause introduces a variable binding
and an optional initial value. The initial values are calculated
in the order in which the with clauses occur.
Iteration control clauses implicitly perform the following actions:
initialize variables;
step variables, generally between each execution of the loop body;
perform termination tests, generally just before the execution of the loop body.