If you want to enable @-expressions in a module that is written in, say, `scheme/base', the old way was to start the file like this:
#reader scribble/reader #lang scheme/base The new way is like this: #lang at-exp scheme/base In general, `at-exp' is a kind of language constructor that installs "@" support (through the readtable) before chaining to a base language. Eventually, DrScheme and other tools will work better on files that start "#lang". The old "#reader" way works only because an S-expression reader happens to be active before "#lang".
