2.12.3 and-let* (SRFI 2)

SRFI 2 provides a form that combines ‘and’ and ‘let*’ for a logically short-circuiting sequential binding operator.

special form: and-let* (clause …) body

Runs through each of the clauses left-to-right, short-circuiting like ‘and’ in that the first false clause will result in the whole ‘and-let*’ form returning false. If a body is supplied, and all of the clauses evaluate true, then the body is evaluated sequentially as if in a ‘begin’ form, and the value of the ‘and-let*’ expression is the value of the last body form, evaluated in a tail position with respect to the ‘and-let*’ expression. If no body is supplied, the value of the last clause, also evaluated in a tail position with respect to the ‘and-let*’ expression, is used instead.

Each clause should have one of the following forms:

‘identifier’

in which case identifier’s value is tested.

‘(expression)’

in which case the value of expression is tested.

‘(identifier expression)’

in which case expression is evaluated, and, if its value is not false, identifier is bound to that value for the remainder of the clauses and the optional body.

Example:

(and-let* ((list (compute-list))
           ((pair? list))
           (item (car list))
           ((integer? item)))
  (sqrt item))