Created
June 6, 2019 17:25
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Parsing JSON to an AST with line/col/offset info with Nearley + moo
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| # Initially based on [https://github.com/kach/nearley/blob/master/examples/json.ne], | |
| # and then reworked to resemble JSON parse from [https://astexplorer.net/] | |
| # JSON [http://www.json.org/] | |
| # Tested with nearleyc v2.16.0 | |
| # interface Pos { | |
| # line: number; | |
| # column: number; | |
| # offset: number; | |
| # } | |
| # interface Loc { | |
| # start: Pos; | |
| # end: Pos; | |
| # } | |
| # interface Node { | |
| # type: string; | |
| # loc: Loc; | |
| # } | |
| # interface PrimitiveLiteral extends Node { | |
| # type: "Literal"; | |
| # value: any; | |
| # raw: string; | |
| # } | |
| # interface Identifier extends Node { | |
| # type: "Identifier"; | |
| # value: any; | |
| # raw: string; | |
| # } | |
| # interface Object extends Node { | |
| # children: Property[]; | |
| # } | |
| # interface Array extends Node { | |
| # children: Value[]; | |
| # } | |
| # type Value = PrimitiveLiteral | Object | Array; | |
| # interface Property extends Node { | |
| # type: "Property"; | |
| # key: Identifier; | |
| # value: Value; | |
| # } | |
| @lexer lexer | |
| json -> _ value _ {% ([,val,]) => val %} | |
| object -> | |
| "{" _ "}" {% compound_empty("Object") %} | |
| | "{" _ property (_ "," _ property):* _ "}" {% compound_children("Object") %} | |
| array -> | |
| "[" _ "]" {% compound_empty("Array") %} | |
| | "[" _ value (_ "," _ value):* _ "]" {% compound_children("Array") %} | |
| value -> | |
| object {% id %} | |
| | array {% id %} | |
| | %true {% primitive_literal() %} | |
| | %false {% primitive_literal() %} | |
| | %null {% primitive_literal() %} | |
| | %number {% primitive_literal() %} | |
| | %string {% primitive_literal() %} | |
| property -> key _ ":" _ value {% property %} | |
| key -> %string {% primitive_literal("Identifier") %} | |
| _ -> null | %space {% d => null %} | |
| @{% | |
| const moo = require("moo"); | |
| const lexer = moo.compile({ | |
| // id: require("./JSIdentifier"), | |
| space: { match: /\s+/, lineBreaks: true }, | |
| number: /-?(?:[0-9]|[1-9][0-9]+)(?:\.[0-9]+)?(?:[eE][-+]?[0-9]+)?\b/, | |
| string: /"(?:\\["bfnrt\/\\]|\\u[a-fA-F0-9]{4}|[^"\\])*"/, | |
| "{": "{", | |
| "}": "}", | |
| "[": "[", | |
| "]": "]", | |
| ",": ",", | |
| ":": ":", | |
| true: "true", | |
| false: "false", | |
| null: "null" | |
| }); | |
| function compound_empty(type) { | |
| return function ([open,,close]) { | |
| return { | |
| type, | |
| children: [], | |
| loc: { start: pos(open), end: pos(close, 1) } | |
| }; | |
| }; | |
| } | |
| function compound_children(type) { | |
| return function ([open,,first,rest,,close]) { | |
| return { | |
| type, | |
| children: [ | |
| first, | |
| ...rest.map(([,,,property]) => property) | |
| ], | |
| loc: { start: pos(open), end: pos(close, 1) } | |
| }; | |
| }; | |
| } | |
| function primitive_literal(type = "Literal") { | |
| return function ([token]) { | |
| return { | |
| type, | |
| value: JSON.parse(token.value), | |
| raw: token.text, | |
| loc: { | |
| start: pos(token), | |
| end: pos(token, token.text.length) | |
| } | |
| }; | |
| }; | |
| } | |
| function property ([key,,,,value]) { | |
| return { | |
| type: "Property", | |
| key, | |
| value, | |
| loc: { | |
| start: key.loc.start, | |
| end: value.loc.end | |
| } | |
| }; | |
| } | |
| function pos({ line, col, offset }, add = 0) { | |
| return { | |
| line, | |
| column: col + add, | |
| offset: offset + add | |
| }; | |
| } | |
| %} |
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