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choice_points [2020/10/08 12:17] – revusky | choice_points [2021/02/08 18:09] (current) – ↷ Links adapted because of a move operation revusky | ||
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I think the simplest way to think about the above cases (for most people, anyway) is just in terms of their analogues in a procedural programming language. The first three cases are effectively binary choices, a choice between entering the expansion inside the parentheses and jumping directly to what follows it. In all of these cases, the expansion within the parentheses is a choice point. The last case is a choice between n options and each of those n sub-expansions is a choice point in the grammar. | I think the simplest way to think about the above cases (for most people, anyway) is just in terms of their analogues in a procedural programming language. The first three cases are effectively binary choices, a choice between entering the expansion inside the parentheses and jumping directly to what follows it. In all of these cases, the expansion within the parentheses is a choice point. The last case is a choice between n options and each of those n sub-expansions is a choice point in the grammar. | ||
- | ==== Zero Or More ==== | + | ==== Zero Or One ==== |
- | A //zero-or-more// is a single (non-looping) choice. If the enclosed expansion matches, we enter it, and if not, we jump directly to whatever follows it. So, if we write: | + | A //zero-or-one// is a single (non-looping) choice. If the enclosed expansion matches, we enter it, and if not, we jump directly to whatever follows it. So, if we write: |
< | < | ||
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===== More than one way to skin a cat... ===== | ===== More than one way to skin a cat... ===== | ||
- | The //definite numerical lookahead// of two tokens worked okay in the above example, but generally speaking, it is a rather crude disposition. The legacy JavaCC tool provides two other ways to specify how we resolve a choice -- when the default resolution is not good enough. In the original, somewhat inaccurate terminology, | + | The //definite numerical lookahead// of two tokens worked okay in the above example, but generally speaking, it is a rather crude disposition. The legacy JavaCC tool provides two other ways to specify how we resolve a choice -- when the default resolution is not good enough. In the original, somewhat inaccurate terminology, |
==== Syntactic Lookahead ==== | ==== Syntactic Lookahead ==== | ||
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In very many common usage cases, the [[up to here]] syntax removes the need to write separate // | In very many common usage cases, the [[up to here]] syntax removes the need to write separate // | ||
- | By the same token, //semantic lookahead//, | + | By the same token, //semantic lookahead//, |
- | A general rule of thumb would be to use [[up to here]] and [[lookbehind]] constructs whenever possible instead of // | + | A general rule of thumb would be to use [[up to here]] and [[contextual_predicates]] constructs whenever possible instead of // |