Figure 20.3: XAldor Debugging Example.
--
-- sieve.as: A prime number sieve to count primes <= n.
--
# include "aldor.as"
sieve(n: SingleInteger): SingleInteger == {
import from Boolean;
local n: SingleInteger;
isprime: PrimitiveArray Boolean := new(n, true);
np := 0;
for p in 2..n | isprime p repeat {
local np: SingleInteger;
np := np + 1;
for i in 2*p..n by p repeat isprime i := false;
}
np
}
litany(): () == {
import IntegerNumberSystem from Integer;
import from Segment SingleInteger;
for i in 1..6 repeat {
n := 10^i;
print << "There are " << sieve n << " primes <= " << n
}
} |
Upon executing the command XAldorcmd -M2 badsieve.as and
selecting the Compile button, the screen shown in
figure 20.4 is displayed.
Two error messages are listed in the Message List Window, and
the contents of the first error message are reflected in the
Message Window. The identifier n
is highlighted in the Source Text Window indicating that the error
has been encountered at this location in the source code.
By selecting the NextMsg button the contents of all screens
are updated to reflect information relating to the second error
message.
In this case, the second error message has related notes,
and so the No Notes button has been replaced by the
See Notes button, as shown in figure 20.5.
Now it is known from the first error message that there is a single identifier
n of type SingleInteger which is being used as both a parameter
and a local variable. The second error message shows a variable np
which has been declared locally after it has already been assigned
a value. So the file badsieve.as can be edited by placing the
cursor into the source text window, removing the redeclaration of
n at line 8, and removing the declaration of np at line
14. These changes can be saved into the file badsieve.as with
the Save button.
After recompiling the file using the Compile button,
the compiler again encounters errors, as can be seen in
figure 20.6.
In this case the first message is caused by an identifier 1,
whose meaning (as shown by selecting Meanings) is a value of type
Integer which has been imported from the
domain Integer.
Using the buttons for the Source Text Window, the neighboring nodes
of the current node can be traversed to give additional information about the
context
in which the identifier 1 is being used. Traversing up the node tree
using the Up button highlights additional text. The Use
button indicates that the identifier 1 is being used in the context of
an iterator. See figure 20.7.
The Home button returns to the node 1, where the current
error message was encountered. Traversing the node path again using
the Prev button and showing the meaning of this node using the
Meanings button indicates that the segment creation operation
(..) used by the iteration uses requires arguments of type
SingleInteger, as can be seen in figure 20.8.
Since it has already been shown that the node 1
is of type Integer, the type conflict which was reported by the
error message has been located.
As it happens, all of the error messages which were reported by this
compilation depend upon this type conflict being resolved.
Additional information about the abstract syntax tree of a program
is provided by the Show button in the Ugly mode.
The node traversal buttons Up, Down,
Next, and Prev can be used to examine the
print function call, for example, as shown in detail in
figure 20.9.
By editing the file badsieve.as to change the statement
import IntegerNumberSystem from Integer; to the statement
import from SingleInteger;, the file now
compiles cleanly and the message No compiler messages! is
returned from the Aldor compiler.
See figure 20.10.
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