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39.3.7 Searching
The procedures for searching elements in lists either accept a
predicate or a comparison object for determining which elements are to
be searched.
find pred lst

Scheme Procedure 
Return the first element of lst which satisfies the predicate
pred and #f if no such element is found.

findtail pred lst

Scheme Procedure 
Return the first pair of lst whose CAR satisfies the
predicate pred and #f if no such element is found.

takewhile pred lst

Scheme Procedure 
takewhile! pred lst

Scheme Procedure 
Return the longest initial prefix of lst whose elements all
satisfy the predicate pred.
takewhile! is allowed, but not required to modify the input
list while producing the result.

dropwhile pred lst

Scheme Procedure 
Drop the longest initial prefix of lst whose elements all
satisfy the predicate pred.

span pred lst

Scheme Procedure 
span! pred lst

Scheme Procedure 
break pred lst

Scheme Procedure 
break! pred lst

Scheme Procedure 
span splits the list lst into the longest initial prefix
whose elements all satisfy the predicate pred, and the remaining
tail. break inverts the sense of the predicate.
span! and break! are allowed, but not required to modify
the structure of the input list lst in order to produce the
result.

any pred lst1 lst2 ...

Scheme Procedure 
Apply pred across the lists and return a true value if the
predicate returns true for any of the list elements(s); return
#f otherwise. The true value returned is always the result of
the first successful application of pred.

every pred lst1 lst2 ...

Scheme Procedure 
Apply pred across the lists and return a true value if the
predicate returns true for every of the list elements(s); return
#f otherwise. The true value returned is always the result of
the final successful application of pred.

listindex pred lst1 lst2 ...

Scheme Procedure 
Return the index of the leftmost element that satisfies pred.

member x lst [=]

Scheme Procedure 
Return the first sublist of lst whose CAR is equal to
x. If x does no appear in lst, return #f .
Equality is determined by the equality predicate =, or
equal? if = is not given.
