Transformers
<transformer spec> -->
(syntax-rules (<identifier>*) <syntax rule>*)
<syntax rule> --> (<pattern> <template>)
<pattern> --> <pattern identifier>
| (<pattern>*)
| (<pattern>+ . <pattern>)
| (<pattern>* <pattern> <ellipsis>)
| #(<pattern>*)
| #(<pattern>* <pattern> <ellipsis>)
| <pattern datum>
<pattern datum> --> <string>
| <character>
| <boolean>
| <number>
<template> --> <pattern identifier>
| (<template element>*)
| (<template element>+ . <template>)
| #(<template element>*)
| <template datum>
<template element> --> <template>
| <template> <ellipsis>
<template datum> --> <pattern datum>
<pattern identifier> --> <any identifier except ...
>
<ellipsis> --> <the identifier ...
>