Clarify execution environment of actions. #531
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This refactors the explanation of actions and predicates and makes a new section for describing the common execution environment.
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This is a wonderful pull request. |
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This is a great idea, never thought of it because I'm used to most of the helpers. Just a few things before I merge:
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README.md
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| offset, there's also a function `offset` that returns just the start offset, | ||
| and a function `range` that returns the array `[start, end]` offsets. | ||
| The predicate should `return` a boolean value. If the result is | ||
| truthy, the match result is `undefined`, otherwise the match is |
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For now match result is result of return-ed expression. And I think that this must stay true and #66 must be closed unresolved.
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@Mingun I just confirmed on pegjs.org/online (PEG.js 0.10) and on runkit.com/futagoza/59b9917124ab7b001102b0f2 (pegjs-dev and Node.js v6) that the behaviour is exactly like it is described, error on failed match and undefined on pass.
I didn't start using predicate's until PEG.js 0.10, and I've never seen a predicate return the result of it's action.
README.md
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| expression as its arguments. The action should return some JavaScript value | ||
| using the `return` statement. This value is considered match result of the | ||
| preceding expression. | ||
| The action shuuld be JavaScript code, and it's executed as a |
README.md
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| The code inside the action can also access location information using the | ||
| `location` function. It returns an object like this: | ||
| * Labels in the preceding expression are available as local |
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It is necessary to specify that from subexpressions labels of parental expressions are available and maybe add an example:
rule = _1:'a' (_2:'c') _3:(_4:'b' { return [_1, _4]; });// _1 also visible, but _2 and _3 not
README.md
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| expression. | ||
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| * `range()` returns an array containing the start and end offsets | ||
| of the preceding expression, such as `[23, 25]`. |
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I think what for predicates can be noted that the start and end a the same.
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I think there was a translation error, I'm guessing you said:
I think that for predicates it can be noted that the
startandendare the same.
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Yes, you right. Thank you for helping me :)
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ok, I think I've resolved all outstanding comments. |
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I've never used |
This refactors the explanation of actions and predicates, and makes a new section for describing the common execution environment.