Method parsePostfix

scripts/rubi/wl-parser.ts:329–373

(expr: Json, wlHead?: string)

  // Handles postfix forms after a head: calls F[a, b][c]…, Part
  // `lst[[1]]`, and derivative marks `F'[x]`.
  private parsePostfix(expr: Json, wlHead?: string): Json {
    for (;;) {
      const t = this.peek();
      if (!t || t.kind !== 'punct') break;
      if (t.value === "'") {
        // F' → Derivative[1][F]; chain for F''
        let order = 0;
        while (this.peek()?.kind === 'punct' && this.peek()!.value === "'") {
          this.next();
          order++;
        }
        expr = [['Derivative', order], wlHead ? mapSymbol(wlHead) : expr];
        wlHead = undefined;
        continue;
      }
      if (t.value !== '[' || t.spaceBefore) break;
      this.next();
      // Part: lst[[i, j]]
      if (this.peek()?.kind === 'punct' && this.peek()!.value === '[') {
        this.next();
        const indices: Json[] = [this.parseExpression(0)];
        while (this.peek()?.kind === 'punct' && this.peek()!.value === ',') {
          this.next();
          indices.push(this.parseExpression(0));
        }
        this.expect(']');
        this.expect(']');
        expr = ['Part', wlHead ? mapSymbol(wlHead) : expr, ...indices];
        wlHead = undefined;
        continue;
      }
      const args: Json[] = [];
      if (!(this.peek()?.kind === 'punct' && this.peek()!.value === ']')) {
        args.push(this.parseExpression(0));
        while (this.peek()?.kind === 'punct' && this.peek()!.value === ',') {
          this.next();
          args.push(this.parseExpression(0));
        }
      }
      this.expect(']');
      expr = wlHead ? mapCall(wlHead, args) : ([expr, ...args] as Json[]);
      wlHead = undefined;
    }
    return expr;
  }
}

function flatBinaryOp(op: string, a: Json, b: Json): Json {