pattern matching

1. A function is defined to take arguments of a particular

type, form or value. When applying the function to its actual

arguments it is necessary to match the type, form or value of

the actual arguments against the formal arguments in some

definition. For example, the function

length [] = 0

length (x:xs) = 1 + length xs

uses pattern matching in its argument to distinguish a null

list from a non-null one.

There are well known algorithm for translating pattern

matching into conditional expressions such as "if" or "case".

E.g. the above function could be transformed to

length l = case l of

[] -@# 0

x:xs -@# 1 : length xs

Pattern matching is usually performed in textual order though

there are languages which match more specific patterns before

less specific ones.

2. Descriptive of a type of language or utility such as awk

or Perl which is suited to searching for strings or patterns

in input data, usually using some kind of regularexpression.

(1994-11-28)