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The Dylan Reference Manual

BNF

General Notes

Dylan syntax can be parsed with an LALR(1) grammar.

This appendix uses some special notation to make the presentation of the grammar more readable.

In the following grammar, some tokens are used multiple ways. For example the hyphen, "-," is punctuation, a unary operator, and a binary operator; also, "method" is a begin-word and a define-body-word. In some parsing implementations such multiple meanings of a token may not be possible. However this is just an implementation issue since the meaning of the grammar is clear. method is used as punctuation in local-methods and method-definition; since method is not a core reserved word, this typically has to be implemented by accepting any macro-name and checking semantically that the word used is "method." The grammar as presented is not obviously LALR(1), since the required changes would tend to obscure the readability for human beings (especially in macro definitions and case-body). The grammar can be made LALR(1) through well-known standard transformations implemented by most parser generators.

Lexical Notes

In the lexical grammar, the various elements that come together to form a single token on the right-hand sides of rules must not be separated by whitespace, so that the end result will be a single token. This is in contrast to the phrase grammar, where each element is already a complete token or a series of complete tokens.

Arbitrary whitespace is permitted between tokens, but it is required only as necessary to separate tokens that might otherwise blend together.

Case is not significant except within character and string literals. The grammars do not reflect this, using one case or the other, but it is still true.