cypher.js

export function parse(text, log=()=>{}) { const r = {}, x = {} // rules defined and traced let left = '', right = text // text parsed and pending let branch = [] // abstract syntax tree in progress const tree = [branch] // Non-Terminal Symbols r.match = () => x.sp() && x.term('match') && x.node() && x.chain() && x.eot() r.node = () => x.ch('(') && x.elem() && x.ch(')') r.chain = () => any(() => x.rel() && x.node() && x.chain()) r.rel = () => one(() => x.in(), () => x.out(), () => x.both()) r.in = () => x.term('<-') && opt(() => x.ch('[') && x.elem() && x.ch(']')) && x.ch('-') r.out = () => x.ch('-') && opt(() => x.ch('[') && x.elem() && x.ch(']')) && x.term('->') r.both = () => x.ch('-') && opt(() => x.ch('[') && x.elem() && x.ch(']')) && x.ch('-') r.elem = () => opt(() => x.bind()) && opt(() => x.ch(':') && x.type()) && opt(() => x.prop()) r.prop = () => x.ch('{') && x.word() && x.ch(':') && x.expr() && x.ch('}') r.expr = () => x.strn() r.bind = () => x.word() r.type = () => x.word() // Terminal Symbols r.word = () => match(/^[A-Za-z][A-Za-z0-9_]*/) && x.sp() r.term = want => right.startsWith(want) && accept(want.length) && keep(want) && x.sp() r.strn = () => x.ch('"') && match(/^[^"]{0,20}/) && x.ch('"') && x.sp() r.ch = char => right.startsWith(char) && accept(1) && keep(char) && x.sp() r.sp = () => match(/^\s*/) r.eot = () => !right.length // Parse Instrumentation for (const op in r) { x[op] = (...args) => { log(`${left}%c${op}%c${right}`,"color:red","color:black"); const here = branch branch = [op] const success = r[op](...args) if (success) here.push(branch) branch = here return success } } // Parser State Updates function match(regex) { const m = right.match(regex) m && accept(m[0].length) && keep(m[0]) return !!m } function keep(text) { branch.push(text) return true } function accept(n) { left += right.substring(0,n) right = right.substring(n) return true } // Backtracking Operators function any (rule) { // rule zero or more times const save = [left,right] if (rule()) { any(rule) } else { [left,right] = save } return true } function opt (rule) { // rule zero or one times const save = [left,right] if (!rule()) { [left,right] = save } return true } function one (...rules) { // first rule of many const save = [left,right] for (const rule of rules) { if(rule()) {return true} [left,right] = save } false } x.match() return tree } export function gen(level, tree, code, log=()=>{}) { const tab = () => ' |'.repeat(level) switch (tree[0]) { case 'sp': case 'ch': case 'term': break case 'bind': case 'type': log(tab(), tree[0], `"${tree[1][1]}"`) code[tree[0]] = tree[1][1] break case 'prop': log(tab(), tree[0], `"${tree[2][1]}"`, tree[4][1][2]) code[tree[0]] = [tree[2][1], tree[4][1][2]] break case 'node': case 'rel': case 'chain': log(tab(), tree[0]) {const sub = {} code[tree[0]] = sub for (const branch of tree.slice(1)) gen(level+1,branch,sub,log)} break case 'in': case 'out': case 'both': log(tab(), tree[0]) code['dir'] = tree[0] for (const branch of tree.slice(1)) gen(level+1,branch,code,log) break case 'match': case 'elem': log(tab(), tree[0]) for (const branch of tree.slice(1)) gen(level+1,branch,code,log) break case 'eot': log(tab(), 'end') break default: log(tab(), 'unknown', tree[0]) } return code } export function check(tally, code, errors) { if(code?.node?.type && errors) { if(!tally.nodes[code.node.type]) { errors.push(`No node of type "${code.node.type}" in the graph.`) } } if(code?.rel?.type && errors) { if(!tally.rels[code.rel.type]) { errors.push(`No relation of type "${code.rel.type}" in the graph.`) } } if(Object.keys(code.chain).length) { check(tally,code.chain, errors) } } export function apply(graph, code) { const nodes = graph.nodes const rels = graph.rels const results = [] for (const node of nodes) { chain(node, code, {}) } return results function chain(node, code, maybe) { if ((!code.node.type || node.type == code.node.type) && (!code.node.prop || node.props[code.node.prop[0]] == code.node.prop[1])) { if (code.node.bind) maybe[code.node.bind] = node if (code.chain.rel) { if (['in','both'].includes(code.chain.rel.dir)) links(node.in, 'from') if (['out','both'].includes(code.chain.rel.dir)) links(node.out, 'to') } else { results.push(maybe) } } function links(rids, dir) { rids.forEach(rid => { if ((!code.chain.rel.type || rels[rid].type == code.chain.rel.type) && (!code.chain.rel.prop || rels[rid].props[code.chain.rel.prop[0]] == code.chain.rel.prop[1])) { maybe = {...maybe} if (code.chain.rel.bind) maybe[code.chain.rel.bind] = rels[rid] chain(nodes[rels[rid][dir]], code.chain, maybe) } }) } } }