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https://github.com/Horizontal42/summarum.git
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flatten parser into a Pratt parser
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Horizontal42
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d3731be6ef
commit
59df3a7264
1 changed files with 149 additions and 162 deletions
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@ -97,6 +97,17 @@ export function parseLine(tokens: Token[], knownVars: Set<string>, line: string)
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return { assign, expr: p.parseSeq() };
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}
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const PREC = {
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CONV: 10,
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BIT: 20,
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ADD: 30,
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MUL: 40,
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UNARY: 50,
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POW: 55,
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POSTFIX: 60,
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};
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class Parser {
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private i = 0;
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constructor(private toks: Token[], private vars: Set<string>) {}
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@ -130,7 +141,7 @@ class Parser {
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}
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if (tk.t === "pctop" && (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is")) && items.length > 0) {
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this.i++;
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const r = this.parseAdd();
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const r = this.parseExpr(PREC.ADD);
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if (r) {
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items = [{ k: "pctop", op: tk.op, l: mk(), r }];
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continue;
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@ -141,7 +152,7 @@ class Parser {
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if (tk.t === "op" && items.length > 0) {
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const save = this.i;
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this.i++;
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const r = tk.op === "plus" || tk.op === "minus" ? this.parseMul() : this.parseUnary();
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const r = tk.op === "plus" || tk.op === "minus" ? this.parseExpr(PREC.MUL) : this.parseExpr(PREC.UNARY);
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if (r) {
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items = [{ k: "bin", op: tk.op, l: mk(), r }];
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continue;
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@ -152,7 +163,7 @@ class Parser {
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if (tk.t === "bitop" && items.length > 0) {
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const save = this.i;
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this.i++;
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const r = this.parseAdd();
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const r = this.parseExpr(PREC.ADD);
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if (r) {
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items = [{ k: "bit", op: tk.op, l: mk(), r }];
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continue;
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@ -161,7 +172,7 @@ class Parser {
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continue;
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}
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const before = this.i;
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const node = this.parseBit();
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const node = this.parseExpr(PREC.BIT);
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if (node) items.push(node);
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if (this.i === before) this.i++; // skip unparsable token
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}
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@ -169,52 +180,144 @@ class Parser {
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return mk();
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}
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/** bitwise level (one flat precedence, left-assoc): & | xor << >> */
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private parseBit(): Node | null {
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let l = this.parseAdd();
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if (!l) return null;
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for (;;) {
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const tk = this.peek();
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if (tk?.t !== "bitop") break;
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const save = this.i;
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/**
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* Pratt parser implementation for expressions.
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*/
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private parseExpr(minPrec: number = 0): Node | null {
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let tk = this.peek();
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if (!tk) return null;
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let lhs: Node | null = null;
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if (tk.t === "op" && tk.op === "minus") {
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this.i++;
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const r = this.parseAdd();
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if (!r) {
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this.i = save;
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break;
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}
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l = { k: "bit", op: tk.op, l, r };
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}
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return l;
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const x = this.parseExpr(PREC.UNARY);
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if (!x) return null;
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lhs = { k: "neg", x };
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} else if (tk.t === "op" && tk.op === "plus") {
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this.i++;
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lhs = this.parseExpr(PREC.UNARY);
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if (!lhs) return null;
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} else {
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lhs = this.parsePrimary();
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}
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/** conversion level: `x in cm`, `x as a % of y`, `x of what is y` */
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private parseConv(): Node | null {
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let l = this.parseBit();
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if (!l) return null;
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if (!lhs) return null;
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for (;;) {
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const tk = this.peek();
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if (tk?.t === "conv") {
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tk = this.peek();
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if (!tk) break;
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if (tk.t === "percent") {
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if (PREC.POSTFIX < minPrec) break;
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this.i++;
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lhs = { k: "pct", x: lhs };
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continue;
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}
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if (tk.t === "bang") {
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if (PREC.POSTFIX < minPrec) break;
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this.i++;
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lhs = { k: "fact", x: lhs };
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continue;
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}
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if (tk.t === "unit") {
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if (PREC.POSTFIX < minPrec) break;
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this.i++;
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lhs = { k: "unit", x: lhs, unit: tk.unit };
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continue;
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}
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if (tk.t === "currency") {
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if (PREC.POSTFIX < minPrec) break;
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this.i++;
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lhs = { k: "curr", x: lhs, code: tk.code };
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continue;
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}
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if (tk.t === "scale") {
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if (PREC.POSTFIX < minPrec) break;
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this.i++;
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lhs = { k: "scale", x: lhs, mult: tk.mult, label: "" };
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continue;
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}
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if (tk.t === "op" && tk.op === "pow") {
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if (PREC.POW < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.POW);
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if (!r) { this.i = save; break; }
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lhs = { k: "bin", op: "pow", l: lhs, r };
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continue;
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}
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if (tk.t === "op" && (tk.op === "mul" || tk.op === "div" || tk.op === "mod")) {
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if (PREC.MUL < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.MUL + 1);
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if (!r) { this.i = save; break; }
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lhs = { k: "bin", op: tk.op, l: lhs, r };
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continue;
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}
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if (tk.t === "pctop" && (tk.op === "of" || tk.op === "off" || tk.op === "on")) {
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if (!(lhs.k === "pct" || lhs.k === "var" || lhs.k === "pctop")) {
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this.i++;
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continue;
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}
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if (PREC.MUL < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.MUL + 1);
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if (!r) { this.i = save; break; }
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lhs = { k: "pctop", op: tk.op, l: lhs, r };
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continue;
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}
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if (tk.t === "lparen" || tk.t === "const" || tk.t === "func" || (tk.t === "word" && this.vars.has(tk.raw))) {
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if (PREC.MUL < minPrec) break;
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const save = this.i;
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const r = this.parseExpr(PREC.MUL + 1);
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if (!r) { this.i = save; break; }
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lhs = { k: "bin", op: "mul", l: lhs, r };
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continue;
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}
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if (tk.t === "op" && (tk.op === "plus" || tk.op === "minus")) {
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if (PREC.ADD < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.ADD + 1);
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if (!r) { this.i = save; break; }
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lhs = { k: "bin", op: tk.op, l: lhs, r };
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continue;
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}
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if (tk.t === "bitop") {
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if (PREC.BIT < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.BIT + 1);
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if (!r) { this.i = save; break; }
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lhs = { k: "bit", op: tk.op, l: lhs, r };
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continue;
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}
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if (tk.t === "conv") {
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if (PREC.CONV < minPrec) break;
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const save = this.i;
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this.i++;
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const target = this.parseTarget();
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if (!target) {
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this.i = save;
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break;
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if (!target) { this.i = save; break; }
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lhs = { k: "conv", x: lhs, target: this.tryHistoricalDate(target) };
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continue;
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}
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l = { k: "conv", x: l, target: this.tryHistoricalDate(target) };
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} else if (tk?.t === "pctop" && (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is"))) {
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if (tk.t === "pctop" && (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is"))) {
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if (PREC.CONV < minPrec) break;
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const save = this.i;
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this.i++;
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const r = this.parseAdd();
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if (!r) break;
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l = { k: "pctop", op: tk.op, l, r };
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} else {
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break;
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}
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}
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return l;
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const r = this.parseExpr(PREC.ADD);
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if (!r) { this.i = save; break; }
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lhs = { k: "pctop", op: tk.op, l: lhs, r };
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continue;
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}
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break;
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}
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return lhs;
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}
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/** If the current token is `pctop(on)` + `datelit`, consume them and attach `onDate`. */
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private tryHistoricalDate(target: ConvTarget): ConvTarget {
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if (target.type !== "currency") return target;
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@ -280,122 +383,6 @@ class Parser {
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return null;
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}
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private parseAdd(): Node | null {
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let l = this.parseMul();
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if (!l) return null;
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for (;;) {
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const tk = this.peek();
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if (tk?.t === "op" && (tk.op === "plus" || tk.op === "minus")) {
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const save = this.i;
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this.i++;
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const r = this.parseMul();
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if (!r) {
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this.i = save;
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break;
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}
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l = { k: "bin", op: tk.op, l, r };
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} else {
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break;
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}
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}
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return l;
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}
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private parseMul(): Node | null {
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let l = this.parseUnary();
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if (!l) return null;
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for (;;) {
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const tk = this.peek();
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if (tk?.t === "op" && (tk.op === "mul" || tk.op === "div" || tk.op === "mod")) {
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const save = this.i;
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this.i++;
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const r = this.parseUnary();
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if (!r) {
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this.i = save;
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break;
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}
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l = { k: "bin", op: tk.op, l, r };
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} else if (tk?.t === "pctop" && (tk.op === "of" || tk.op === "off" || tk.op === "on")) {
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// of/off/on only make sense with a percent on the left ("20% of x");
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// otherwise the word is prose noise ("5 on coffee")
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if (!(l.k === "pct" || l.k === "var" || l.k === "pctop")) {
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this.i++;
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continue;
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}
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const save = this.i;
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this.i++;
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const r = this.parseUnary();
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if (!r) {
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this.i = save;
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break;
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}
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l = { k: "pctop", op: tk.op, l, r };
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} else if (
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tk &&
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(tk.t === "lparen" || tk.t === "const" || tk.t === "func" || (tk.t === "word" && this.vars.has(tk.raw)))
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) {
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// implicit multiplication: 2(3+4), 2pi, 2x
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const save = this.i;
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const r = this.parseUnary();
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if (!r) {
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this.i = save;
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break;
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}
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l = { k: "bin", op: "mul", l, r };
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} else {
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break;
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}
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}
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return l;
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}
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private parseUnary(): Node | null {
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const tk = this.peek();
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if (tk?.t === "op" && tk.op === "minus") {
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this.i++;
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const x = this.parseUnary();
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return x ? { k: "neg", x } : null;
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}
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if (tk?.t === "op" && tk.op === "plus") {
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this.i++;
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return this.parseUnary();
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}
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return this.parsePostfix();
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}
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private parsePostfix(): Node | null {
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let x = this.parsePrimary();
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if (!x) return null;
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for (;;) {
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const tk = this.peek();
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if (!tk) break;
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if (tk.t === "percent") {
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this.i++;
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x = { k: "pct", x };
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} else if (tk.t === "bang") {
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this.i++;
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x = { k: "fact", x };
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} else if (tk.t === "unit") {
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this.i++;
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x = { k: "unit", x, unit: tk.unit };
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} else if (tk.t === "currency") {
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this.i++;
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x = { k: "curr", x, code: tk.code };
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} else if (tk.t === "scale") {
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this.i++;
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x = { k: "scale", x, mult: tk.mult, label: "" };
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} else if (tk.t === "op" && tk.op === "pow") {
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this.i++;
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const r = this.parseUnary();
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if (!r) break;
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x = { k: "bin", op: "pow", l: x, r };
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} else {
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break;
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}
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}
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return x;
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}
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private parsePrimary(): Node | null {
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const tk = this.peek();
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if (!tk) return null;
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@ -431,7 +418,7 @@ class Parser {
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this.i++;
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const args: Node[] = [];
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for (;;) {
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const arg = this.parseConv();
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const arg = this.parseExpr(PREC.CONV);
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if (arg) args.push(arg);
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const nx = this.peek();
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if (nx?.t === "semicolon") {
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@ -452,12 +439,12 @@ class Parser {
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// `sqrt 16` / `square root of 16` — the "of" is decorative
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const nx = this.peek();
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if (nx?.t === "pctop" && nx.op === "of") this.i++;
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const arg = this.parseUnary();
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const arg = this.parseExpr(PREC.UNARY);
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return arg ? { k: "call", name, args: [arg] } : null;
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}
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case "lparen": {
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this.i++;
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const inner = this.parseConv();
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const inner = this.parseExpr(PREC.CONV);
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if (this.peek()?.t === "rparen") this.i++;
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return inner;
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}
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