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Perl provides three loop control keywords that all accept an optional loop label as an argument. If no label is specified, the keywords act on the innermost loop. Within nested loops, the use of labels enables control to move from an inner loop to an outer one, or out of the outer loop altogether.
In Perl, foreach (which is equivalent to the shorter for) can be used to traverse elements of a list. The expression which denotes the collection to loop over is evaluated in list-context and each item of the resulting list is, in turn, aliased to the loop variable. List literal example:
List comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions.
A hash variable is marked by a % sigil, to distinguish it from scalar, array, and other data types. A hash literal is a key-value list, with the preferred form using Perl's => token, which is semantically mostly identical to the comma and makes the key-value association clearer:
Array.iter (fun item-> instructions) array or List.iter (fun item-> instructions) list: F#: while condition do Tab ↹instructions — for i = first to last do Tab ↹instructions: foritem in set do Tab ↹instructions or Seq.iter (fun item-> instructions) set: Standard ML: while condition do ( instructions) — Array.app (fn item ...
The following list contains syntax examples of how a range of element of an array can be accessed. In the following table: first – the index of the first element in the slice; last – the index of the last element in the slice; end – one more than the index of last element in the slice; len – the length of the slice (= end - first)
A list comprehension has the same syntactic components to represent generation of a list in order from an input list or iterator: A variable representing members of an input list. An input list (or iterator). An optional predicate expression. And an output expression producing members of the output list from members of the input iterable that ...
Perl programmers may initialize a hash (or associative array) from a list of key/value pairs. If the keys are separated from the values with the => operator (sometimes called a fat comma), rather than a comma, they may be unquoted (barewords [5]). The following lines are equivalent: