Transformers (Revised7.0 Report on the Algorithmic Language Scheme (Unofficial))

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7.1.5 Transformers ¶

Note: Though this grammar does not say so, a top-level syntax-rules pattern must be a list pattern, not a vector pattern or an identifier pattern.

⟨transformer spec⟩ ⟶
    (syntax-rules (⟨identifier⟩*) ⟨syntax rule⟩*)
    | (syntax-rules ⟨identifier⟩ (⟨identifier⟩*) ⟨syntax rule⟩*)
⟨syntax rule⟩ ⟶ (⟨pattern⟩ ⟨template⟩)
⟨pattern⟩ ⟶ ⟨pattern identifier⟩
    | ⟨underscore⟩
    | (⟨pattern⟩*)
    | (⟨pattern⟩+ . ⟨pattern⟩)
    | (⟨pattern⟩* ⟨pattern⟩ ⟨ellipsis⟩ ⟨pattern⟩*)
    | (⟨pattern⟩* ⟨pattern⟩ ⟨ellipsis⟩ ⟨pattern⟩* . ⟨pattern⟩)
    | #(⟨pattern⟩*)
    | #(⟨pattern⟩* ⟨pattern⟩ ⟨ellipsis⟩ ⟨pattern⟩)
    | ⟨pattern datum⟩
⟨pattern datum⟩ ⟶ ⟨string⟩
    | ⟨character⟩
    | ⟨boolean⟩
    | ⟨number⟩
    | ⟨bytevector⟩
⟨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⟩ ⟶ ⟨an identifier defaulting to ‘...’⟩
⟨underscore⟩ ⟶ ⟨the identifier ‘_’⟩