Lambda the Ultimate Block

ブロックとしてのlambda
   (with-input-from-file "file"
     (lambda ()
       ... 処理 ...))
  Cf. File.open("file", "r") { ... 処理 ... }

   (define (with-input-from-file filename proc)
     { current-input-port ← filenameをopen }
     (let ((result (proc)))
       { fileをclose }
       result))