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// Node objects are immutable |
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// Also immutable are: properties, attributes, children, terminals, and any arrays |
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// Immutable trees can be cached as valid with regard to a particular grammar! |
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let freeze = (node) => Object.freeze(Object.seal(node)); |
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|
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// Helpers for constructing agAST trees |
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let t = { |
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// Tokens are really just nodes with non-ref children |
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token: (type, str, attributes = {}) => t.node(type, [t.str([str])], {}, attributes), |
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node: (type, children = [], properties = {}, attributes = {}) => |
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freeze({ |
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// nodes are truly monomorphic, making tools faster |
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...type, |
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children: freeze(children), |
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properties: freeze(properties), |
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attributes: freeze(attributes), |
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}), |
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id: ([str]) => { |
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const { 0: language, 1: type } = str.split(':'); |
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return { language, type }; |
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}, |
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// These are the types possible in the children array: |
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ref: ([property]) => freeze({ type: 'Reference', value: property }), |
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gap: ([property]) => freeze({ type: 'Gap', value: property }), |
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str: ([str]) => freeze({ type: 'String', value: str }), |
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trivia: ([str]) => freeze({ type: 'Trivia', value: str }), |
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esc: (raw, cooked) => freeze({ type: 'Escape', value: { raw, cooked } }), |
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}; |
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// Input: for (\u0061sync of []); |
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let tree = t.node( |
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// Language:Production |
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t.id`JS:ForOfStatement`, |
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|
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// The children array creates a total ordering of all nodes and tokens |
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// It ensures that any document can be printed without needing a grammar |
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[ |
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t.ref`for`, |
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t.trivia` `, |
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t.ref`open`, |
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t.ref`left`, |
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t.trivia` `, |
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t.ref`of`, |
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t.trivia` `, |
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t.ref`right`, |
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t.ref`close`, |
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t.ref`semi`, |
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], |
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// The properties object allows for fast named lookups of nodes and tokens |
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{ |
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for: t.token(t.id`JS:Keyword`, 'for'), |
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open: t.token(t.id`JS:Punctuator`, '('), |
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left: t.node( |
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t.id`JS:Identifier`, |
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[ |
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// Escapes have internal structure, but it is essentially |
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// embedded "onto" them not "into" them |
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t.esc('\\u0061', 'a'), |
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t.str`sync`, |
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], |
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), |
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of: t.token(t.id`JS:Keyword`, 'of'), |
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right: t.node(t.id`JS:ArrayExpression`, [t.ref`open`, t.ref`close`], { |
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open: t.token(t.id`JS:Punctuator`, '['), |
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close: t.token(t.id`JS:Punctuator`, ']'), |
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}), |
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close: t.token(t.id`JS:Punctuator`, ')'), |
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semi: t.token(t.id`JS:Punctuator`, ';'), |
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}, |
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); |
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console.log(JSON.stringify(tree, undefined, 2)); |
