(m4.info)Improved exch

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17.1 Solution for 'exch'
========================

The 'exch' macro (Note: Arguments) as presented requires clients to
double quote their arguments.  A nicer definition, which lets clients
follow the rule of thumb of one level of quoting per level of
parentheses, involves adding quotes in the definition of 'exch', as
follows:

     define(`exch', ``$2', `$1'')
     =>
     define(exch(`expansion text', `macro'))
     =>
     macro
     =>expansion text