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refactor: use switch statement in parser loop for readability (#101)
Replaces the deeply nested if-chain inside the Pratt parser loop in `src/engine/parser.ts` with a `switch` statement over token types. Introduces a labeled `loop: for(;;)` to maintain accurate `continue`/`break` semantics while greatly enhancing the visual parsing and extensibility of the logic without hurting evaluation speed. Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
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1 changed files with 120 additions and 103 deletions
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@ -217,114 +217,131 @@ class Parser {
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if (!lhs) return null;
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for (;;) {
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loop: for (;;) {
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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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switch (tk.t) {
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case "percent": {
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if (PREC.POSTFIX < minPrec) break loop;
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this.i++;
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continue;
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lhs = { k: "pct", x: lhs };
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continue loop;
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}
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case "bang": {
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if (PREC.POSTFIX < minPrec) break loop;
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this.i++;
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lhs = { k: "fact", x: lhs };
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continue loop;
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}
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case "unit": {
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if (PREC.POSTFIX < minPrec) break loop;
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this.i++;
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lhs = { k: "unit", x: lhs, unit: tk.unit };
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continue loop;
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}
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case "currency": {
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if (PREC.POSTFIX < minPrec) break loop;
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this.i++;
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lhs = { k: "curr", x: lhs, code: tk.code };
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continue loop;
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}
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case "scale": {
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if (PREC.POSTFIX < minPrec) break loop;
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this.i++;
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lhs = { k: "scale", x: lhs, mult: tk.mult, label: "" };
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continue loop;
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}
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case "op": {
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switch (tk.op) {
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case "pow": {
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if (PREC.POW < minPrec) break loop;
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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 loop; }
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lhs = { k: "bin", op: "pow", l: lhs, r };
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continue loop;
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}
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case "mul":
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case "div":
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case "mod": {
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if (PREC.MUL < minPrec) break loop;
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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 loop; }
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lhs = { k: "bin", op: tk.op, l: lhs, r };
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continue loop;
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}
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case "plus":
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case "minus": {
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if (PREC.ADD < minPrec) break loop;
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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 loop; }
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lhs = { k: "bin", op: tk.op, l: lhs, r };
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continue loop;
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}
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}
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break loop;
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}
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case "pctop": {
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if (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 loop;
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}
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if (PREC.MUL < minPrec) break loop;
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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 loop; }
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lhs = { k: "pctop", op: tk.op, l: lhs, r };
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continue loop;
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}
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if (tk.op.startsWith("as_pct") || tk.op.endsWith("what_is")) {
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if (PREC.CONV < minPrec) break loop;
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const save = this.i;
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this.i++;
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const r = this.parseExpr(PREC.ADD);
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if (!r) { this.i = save; break loop; }
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lhs = { k: "pctop", op: tk.op, l: lhs, r };
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continue loop;
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}
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break loop;
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}
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case "lparen":
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case "const":
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case "func":
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case "word": {
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if (tk.t === "word" && !this.vars.has(tk.raw)) break loop;
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if (PREC.MUL < minPrec) break loop;
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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 loop; }
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lhs = { k: "bin", op: "mul", l: lhs, r };
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continue loop;
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}
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case "bitop": {
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if (PREC.BIT < minPrec) break loop;
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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 loop; }
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lhs = { k: "bit", op: tk.op, l: lhs, r };
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continue loop;
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}
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case "conv": {
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if (PREC.CONV < minPrec) break loop;
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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) { this.i = save; break loop; }
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lhs = { k: "conv", x: lhs, target: this.tryHistoricalDate(target) };
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continue loop;
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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) { 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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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.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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