Swift User Guide
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Statements which deal with the array as a whole will often wait for the array to be closed before executing (thus, a closed array
is the equivalent of a non-array type being assigned). However, a foreach statement will apply its body to elements of an array as
they become known. It will not wait until the array is closed.
Consider this script:
file a[];
file b[];
foreach v,i in a {
b[i] = p(v);
}
a[0] = r();
a[1] = s();
Initially, the foreach statement will have nothing to execute, as the array a has not been assigned any values. The procedures r
and s will execute. As soon as either of them is finished, the corresponding invocation of procedure p will occur. After both r and
s have completed, the array a will be closed since no other statements in the script make an assignment to a.
2.5 Compound procedures
As with many other programming languages, procedures consisting of Swift script can be defined. These differ from the pre-
viously mentioned procedures declared with the app keyword, as they invoke other Swift procedures rather than a component
program.
(file output) process (file input) {
file intermediate;
intermediate = first(input);
output = second(intermediate);
}
file x <"x.txt">;
file y <"y.txt">;
y = process(x);
This will invoke two procedures, with an intermediate data file named anonymously connecting the first and second procedures.
Ordering of execution is generally determined by execution of app procedures, not by any containing compound procedures. In
this code block:
(file a, file b) A() {
a = A1();
b = A2();
}
file x, y, s, t;
(x,y) = A();
s = S(x);
t = S(y);
then a valid execution order is: A1 S(x) A2 S(y). The compound procedure A does not have to have fully completed for its return
values to be used by subsequent statements.
2.6 More about types
Each variable and procedure parameter in Swift script is strongly typed. Types are used to structure data, to aid in debugging and
checking program correctness and to influence how Swift interacts with data.
The image type declared in previous examples is a marker type. Marker types indicate that data for a variable is stored in a single
file with no further structure exposed at the Swift script level.
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