4.13 Macro Formal Parameters

Formal parameters can appear in the expressions forming macro bodies in accordance with the syntax rules defined above. A formal parameter expands to the text of the expansion of its corresponding actual parameter. There is nothing preventing a formal parameter being provided as part of an expression that forms an actual parameter. In that happens, the formal parameter is bound to the actual parameter of the calling macro, not the called macro. After the following definitions,

@$@<One@>@(@1@)=@{A walrus in @1 is a walrus in vain.@}
@$@<Two@>@(@1@)=@{@<One@>@(S@1n@)@}

the call

@<Two@>@(pai@)

will result in the expansion

A walrus in Spain is a walrus in vain.