# L015

> expressions or blocks nest too deeply

**Severity** Error

Expressions and blocks may nest at most 128 levels: parentheses inside parentheses, a very long chain like `a + b + c + …`, `if` inside `if`, or a long `else if` ladder. Scripts are shared between traders, so the compiler refuses source that would exhaust the stack of the computer compiling it. Real scripts stay far below the limit; generated code is the usual cause. After this error the rest of the file is not checked.

Split the expression into `let` steps, move parts into functions, or turn an `else if` ladder into a `match`.

## Failing example

```flowscope
script "Too deep"
data chart = subscribe(data.ohlcv)
plot p = plot.line(title: "P")
on chart.close {
  p.plot(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((chart.close ?? 0.0)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
}
```

## Fixed example

```flowscope
script "Too deep"
data chart = subscribe(data.ohlcv)
plot p = plot.line(title: "P")
on chart.close {
  let close = chart.close ?? 0.0
  p.plot(close)
}
```