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In the Perl programming language, autovivification is the automatic creation of new arrays and hashes as required every time an undefined value is dereferenced. Perl autovivification allows a programmer to refer to a structured variable, and arbitrary sub-elements of that structured variable, without expressly declaring the existence of the ...
Perl 5 has built-in, language-level support for associative arrays. Modern Perl refers to associative arrays as hashes; the term associative array is found in older documentation but is considered somewhat archaic. Perl 5 hashes are flat: keys are strings and values are scalars.
is how one would use Fortran to create arrays from the even and odd entries of an array. Another common use of vectorized indices is a filtering operation. Consider a clipping operation of a sine wave where amplitudes larger than 0.5 are to be set to 0.5. Using S-Lang, this can be done by
Impatient Perl – for readers with previous programming experience. Learn Perl in about a week. Learning Perl the Hard Way – for people who know another programming language. Higher-Order Perl – advanced programming in Perl; Perl phrasebook – compare equivalent examples of Perl and Python code, on the Python Wiki; Perl scripts. Perl ...
^d Although Perl doesn't have records, because Perl's type system allows different data types to be in an array, "hashes" (associative arrays) that don't have a variable index would effectively be the same as records. ^e Enumerations in this language are algebraic types with only nullary constructors
The Perl Cookbook is written by Tom Christiansen and Nathan Torkington, and published by O'Reilly. The Perl Cookbook inspired the PLEAC (Programming Language Examples Alike Cookbook) website, which translated the code snippets in the Perl Cookbook into other languages: Python, Ruby, Guile, Tcl, Java, and beyond. O'Reilly went on to publish ...
The empty hash {} is also true; in this context {} is not an empty block, because perl -e 'print ref {}' returns HASH. Evaluated boolean expressions are also scalar values. The documentation does not promise which particular value of true or false is returned. Many boolean operators return 1 for true and the empty-string for false.
Folds can be regarded as consistently replacing the structural components of a data structure with functions and values. Lists, for example, are built up in many functional languages from two primitives: any list is either an empty list, commonly called nil ([]), or is constructed by prefixing an element in front of another list, creating what is called a cons node ( Cons(X1,Cons(X2,Cons ...