Wikipedia: "Parsing"

Read the following three paragraphs: "Programming languages," "Overview of the process," and "Types of Parsers." Requirements of a parser include: build internal representation of the input tokens (which come from the scanner); check that the input string of tokens is legal in the language of the compiler (i.e., that it can be derived from the start symbol); and determine the derivation steps for the input string of tokens. In addition, the parser should be reliable, efficient (how efficient depends on the intended use), user friendly (i.e., provide clear, accurate messages), and supportable (assuming that the parser will be used for a long time).

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