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A pattern is a string of characters intended to match one or more user inputs. A literal pattern like WHAT IS YOUR NAME will match only one input, ignoring case: "what is your name". But patterns may also contain wildcards, which match one or more words. A pattern like WHAT IS YOUR * will match an infinite number of inputs, including "what is ...
"One should be careful when reasoning with such non-classic logics, as basic intuitions may deceive." [1] When interpreting matching logic (that is, defining its semantic meaning), a pattern is modeled with a power set. The statement's interpretation is the set of values that match the pattern.
Production systems may vary on the expressive power of conditions in production rules. Accordingly, the pattern matching algorithm that collects production rules with matched conditions may range from the naive—trying all rules in sequence, stopping at the first match—to the optimized, in which rules are "compiled" into a network of inter-related conditions.
Here, the first n is a single variable pattern, which will match absolutely any argument and bind it to name n to be used in the rest of the definition. In Haskell (unlike at least Hope ), patterns are tried in order so the first definition still applies in the very specific case of the input being 0, while for any other argument the function ...
Generalizations of the same idea can be used to find more than one match of a single pattern, or to find matches for more than one pattern. To find a single match of a single pattern, the expected time of the algorithm is linear in the combined length of the pattern and text, although its worst-case time complexity is the product of the two ...
1 2 3 Case-expressions in Haskell and match-expressions in F# and Haskell allow both switch-case and pattern matching usage. ^ In a Ruby case construct, regular expression matching is among the conditional flow-control alternatives available. For an example, see this Stack Overflow question. 1 2 SQL has two similar constructs that fulfill both ...
Syntactic pattern recognition can be used instead of statistical pattern recognition if clear structure exists in the patterns. One way to present such structure is via strings of symbols from a formal language. In this case, the differences in the structures of the classes are encoded as different grammars.
In addition to a guard attached to a pattern, pattern guard can refer to the use of pattern matching in the context of a guard. In effect, a match of the pattern is taken to mean pass. This meaning was introduced in a proposal for Haskell by Simon Peyton Jones titled A new view of guards in April 1997 and was used in the implementation of the ...