|SAS Macro Language: Reference|
The macro language is a character-based language. Even variables that appear to be numeric are generally treated as character variables (except during expression evaluation). Therefore, the macro processor enables you to generate all sorts of special characters as text; but because the macro language is composed of some of the same special characters, an ambiguity often arises: should the macro processor interpret a particular special character (for example, a semicolon or % sign) or a mnemonic (for example, GE or AND) as text or as a symbol in the macro language? Macro quoting functions resolve these ambiguities by masking the significance of special characters so the macro processor does not misinterpret them.
The following special characters and mnemonics may require masking when they appear in text strings:
|Understanding Why Macro Quoting is Necessary|
Macro quoting functions tell the macro processor to interpret special characters and mnemonics as text rather than as part of the macro language. If you did not use a macro quoting function to mask the special characters, the macro processor or the rest of the SAS System might give the character a meaning you did not intend. Here are some examples of the kinds of ambiguities that can arise when text strings contain special characters and mnemonics:
%signa call to the macro SIGN or a phrase "percent sign"?
Macro quoting functions enable you to clearly indicate to the macro processor how it is to interpret special characters and mnemonics.
Here is an example, using the simplest macro quoting function, %STR. Suppose you want to assign a PROC PRINT statement and a RUN statement to the macro variable PRINT. Here is the erroneous statement:
%let print=proc print; run;; /* ERROR */
This code is ambiguous. Are the semicolons that follow PRINT and RUN part of the value of the macro variable PRINT, or does one of them end the %LET statement? If you do not tell the macro processor what to do, it interprets the semicolon after PRINT as the end of the %LET statement; the value of the PRINT macro variable is
The rest of the characters (RUN;;) are simply the next part of the program.
To avoid the ambiguity and correctly assign the value of PRINT, you must mask the semicolons with the macro quoting function %STR, as follows:
%let print=%str(proc print; run;);
|Understanding Macro Quoting Functions|
The following macro quoting functions are most commonly used:
For the paired macro quoting functions, the function beginning with NR affects the same category of special characters that are masked by the plain macro quoting function as well as ampersands and percent signs. In effect, the NR functions prevent macro and macro variable resolution. To help you remember which does which, try associating the NR in the macro quoting function names with the words "not resolved" -- that is, macros and macro variables are not resolved when you use these functions.
The macro quoting functions with B in their names are useful for macro quoting unmatched quotation marks and parentheses. As a help for remembering this, try associating B with "by itself".
The %SUPERQ macro quoting function is unlike the other macro quoting functions in that it does not have a mate and works differently than the other macro quoting functions. See Using %SUPERQ for more information on the %SUPERQ macro quoting function.
The macro quoting functions can also be divided into three types, depending on when they take effect:
|compilation functions||cause the macro processor to interpret special characters as text in a macro program statement in open code or while compiling (constructing) a macro. The %STR and %NRSTR functions are compilation functions.|
|execution functions||cause the macro processor to treat as text special
characters that result from resolving a macro expression (such as a macro
variable reference, a macro invocation, or the argument of an implicit %EVAL
function). They are called execution functions because resolution occurs during
macro execution or during execution of a macro program statement in open code.
The macro processor resolves the expression as far as possible, issues any
warning messages for macro variable references or macro invocations it cannot
resolve, and quotes the result. The %BQUOTE and %NRBQUOTE functions are execution
An implicit %EVAL function is one that is caused by another macro statement, such as a %DO %TO statement. An explicit %EVAL function is one that is directly called by macro code.
|function that prevents resolution||causes the macro processor to treat the value of
a macro variable as a "picture" during macro execution. It treats
the value as text, without beginning the process of resolution. The %SUPERQ
function prevents resolution of a macro variable's value.
The %SUPERQ function takes as its argument a macro variable name (or a macro expression that yields a macro variable name). The argument must not be a reference to the macro variable whose value you are masking; that is, do not include the & before the name.
Note: Two other execution macro quoting functions exist,
%QUOTE and %NRQUOTE. They are useful for unique macro quoting needs and for
compatibility with older macro applications. For more information on these
two macro quoting functions, refer to Chapter 13, "Macro Language Dictionary."
|Passing Parameters That Contain Special Characters and Mnemonics|
Using an execution macro quoting function in the macro definition
is the simplest and best way to have the macro processor accept resolved values
that may contain special characters. However, if you discover that you need
to pass parameter values such as
or when a macro has not
been defined with an execution macro quoting function, you can do so by masking
the value in the macro invocation. The logic of the process is as follows:
For example, suppose a macro named ORDERX does not use the %BQUOTE function.
You can pass the value
or to the ORDERX macro with the following
However, placing the macro quoting function in the macro definition makes the macro much easier for you to invoke.
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