| var SExprParser = { | |
| parse: function(input) { | |
| input = input.trim(); | |
| if (!input) return null; | |
| return this._readAtom(input, 0).value; | |
| }, | |
| _readAtom: function(input, pos) { | |
| while (pos < input.length && input[pos] === ' ') pos++; | |
| if (pos >= input.length) return { value: null, pos: pos }; | |
| if (input[pos] === '(') { | |
| return this._readList(input, pos + 1); | |
| } else if (input[pos] === '"') { | |
| return this._readString(input, pos + 1); | |
| } else { | |
| return this._readSymbol(input, pos); | |
| } | |
| }, | |
| _readList: function(input, pos) { | |
| var items = []; | |
| while (pos < input.length) { | |
| while (pos < input.length && input[pos] === ' ') pos++; | |
| if (pos >= input.length) break; | |
| if (input[pos] === ')') return { value: items, pos: pos + 1 }; | |
| var result = this._readAtom(input, pos); | |
| items.push(result.value); | |
| pos = result.pos; | |
| } | |
| return { value: items, pos: pos }; | |
| }, | |
| _readString: function(input, pos) { | |
| var start = pos; | |
| while (pos < input.length && input[pos] !== '"') pos++; | |
| return { value: input.substring(start, pos), pos: pos + 1 }; | |
| }, | |
| _readSymbol: function(input, pos) { | |
| var start = pos; | |
| while (pos < input.length && '() '.indexOf(input[pos]) === -1) pos++; | |
| var raw = input.substring(start, pos); | |
| var num = Number(raw); | |
| if (!isNaN(num) && raw !== '') return { value: num, pos: pos }; | |
| return { value: raw, pos: pos }; | |
| }, | |
| toString: function(expr) { | |
| if (expr === null) return 'nil'; | |
| if (typeof expr === 'string') return '"' + expr + '"'; | |
| if (typeof expr === 'number') return String(expr); | |
| if (Array.isArray(expr)) { | |
| return '(' + expr.map(this.toString.bind(this)).join(' ') + ')'; | |
| } | |
| return String(expr); | |
| } | |
| }; | |