On this page:
#%expression

2.4 Expression Wrapper: #%expression

syntax

(#%expression expr)

Produces the same result as expr. The only use of #%expression is to force the parsing of a form as an expression.

Examples:

> (#%expression (+ 1 2))

3

> (#%expression (define x 10))

eval:8:0: define: not allowed in an expression context

  in: (define x 10)