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<TITLE>6.4 The Case of the Small Function</TITLE>
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<P><FONT SIZE="5">6.4 The Case of the Small Function</FONT><BR>
<P>Often, when programming, there is a need for a code
abstraction facility that
operates at the text level. If the statement
"<TT>a:=3;</TT>" occurs often, it may be best simply to
repeat it verbatim. If a sequence of one hundred statements
is repeated often, it is normal to remove the code to a
function and replace the occurrences by a function call.
However, in between these two extremes are cases where a
particular sequence of code is long enough and appears often
enough to be troublesome, but which is bound so messily to
its environment as to make a function call cumbersome.
<P>For example, the following line of statements
(referring to five variables declared <I>local</I> to a
function) might appear ten times in a function:
<P>
<PRE>
a=b*3.14159; c=d % 256; e=e+1;
</PRE>
<P>Now the "normal" rule of programming says that
these statements should be placed in a procedure (also
called a "function" in the C programming language
used in this example), but here five local variables are
used. Use of a procedure (function) would result in a
procedure definition looking something like:
<P>
<PRE>
void frobit(a,b,c,d,e)
float *a,b;
int *c,d;
unsigned *e;
{*a=b << 8; *c=d % 256; *e=*e+1;}
</PRE>
<P>and a procedure call something like
<P>
<PRE>
frobit(&a,b,&c,d,&e);
</PRE>
<P>This might be workable in a language that allowed
formal parameters to be specified to be bound only to
particular variables. Similarly, it might be possible to
avoid the parameter list in languages that support local
procedures that can access non-local variables (such as
Pascal). However, in our example here, in the
C programming language, these options are not available, and
so we must either create a function with five parameters, or
use the C macro preprocessor (the
best solution). FunnelWeb provides the same macro facility
for languages that do not have a built-in preprocessor.
<P>In particularly speed-stressed applications, the
programmer may be reluctant to remove code to a procedure
because of the procedure-call overhead. FunnelWeb macros can help there too.
<P>In summary, there sometimes arises in programming
situations where the cost of defining a procedure is higher
than the benefits it will bestow. Common reasons for this
are the run-time procedure overhead and the messy binding
problems caused by removing
target code from its target context. FunnelWeb can help in
these situations by allowing the programmer to define a text
macro. This avoids all the problems and provides an
additional incentive for the programmer to describe the
piece of code so isolated.
<P>
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