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Why do I get errors with my local macros?

Title   The correct delimiter for local macros
Author William Gould, StataCorp

By far the most common mistake when users begin to program in Stata is failing to recognize that the local macros have different single quotes as delimiters. When you want to access the contents of a local macro, you must have the following three things:

  1. A leading single left quote. This key is usually located under the ˜ key (on English keyboards) at the upper left side of the keyboard.
  2. The macro name.
  3. A trailing single right quote. This key is under the " key located (on English keyboards) next to the Enter key.

Use of local macros should be performed as

        . local age = 32
        . display "My age is `age'"

There are certainly more advanced uses for local macros, and you can even embed them in their definition.

        . local a = 1
        . local b`a' = 2
        . local c`b' = 3

So, what macros did I just define? What if I typed

        . local a = 1
        . local `a' = 2
        . local b`d'`j' = 5

What would be defined? It is not too hard to figure out if you remember that Stata performs the following operations when it reads a command:

  • If a command contains macro references, then all references are resolved before the command is interpreted.
  • Resolution of macros occurs from left to right.

So, in the above examples, we can see

        . local a = 1

assigns the character 1 to the macro named a. The next command becomes

        . local b1 = 2

and assigns the character 2 to the macro named b1. The next command becomes

        . local c2 = 3

and assigns the character 3 to the macro named c2. In the next collection of macros, we see the same first command. The following statement becomes

        . local 1 = 2

and assigns the character 2 to the macro named 1! Stata allows you to have macros that are named with numbers. There are times when this really turns out to be convenient. The final statement becomes

        . local b = 5

and assigns the character 5 to the macro named b. This illustrates that Stata does not mind if you attempt to refer to a macro that has not yet had its contents set. It simply returns what the contents are, which is nothing.