Any signficant project in any language has a &quot;dictionary&quot; of custom identifiers, whose vocabulary you have to learn if you want to become a maintainer.<p>The thousand functions in a big C program are just as much a language, as some Lisp macros.<p>The functions all do something. That something isn&#x27;t &quot;transform the code&quot;, but that doesn&#x27;t matter; if you&#x27;re looking at the function call and don&#x27;t know what it does, you&#x27;re just as lost.<p>Basically, if you&#x27;re reading Lisp, you go from &quot;outside in&quot; and just <i>assume</i> that everything you see whose definition you are not familiar with is a macro.<p>Well-behaved code follows certain unwritten conventions. For instance, it avoids creating confusion by exhibiting multiple completely independent uses of the same symbols in the same scope.  So for instance if we have (frobozz a b) wrapped in a lexical scope where we have (let (a b) ...) in effect, this well-behavedness principle tells us that the a and b symbols in (frobozz a b) refer to these variables. So, we can probably lay aside our suspicion that, for instance, frobozz is redefining some unrelated a in terms of some unrelated b. However, frobozz might be a macro; so we can&#x27;t cast aside our suspicion that either a or b has its value clobbered.  (Same in Pascal or C++, with ordinary functions: frobozz(a, b) could take VAR parameters or references, respectively).