عملگرهای تنبل، E3302 و W3302

// The right side of "and" runs only when the left side is true, and so does an arm of "if ... then ... else" that is not chosen: neither is read at all.
// That lets a guard protect a read that would fail. The array holds the rises of the close; its tenth item does not exist until ten rises have been seen,
// and the size test on the left keeps the read on the right from ever failing.
indicator "Guarded read"
    edition = 1
    display = pane

state gains: array<float> = array<float>()
if close > close[1]
    gains.push(close - close[1])
let tenth_is_big = gains.size() > 9 and gains.at(9) > 2
let newest = if gains.size() > 0 then gains.last() else 0.0
let flag = if tenth_is_big then 1 else 0
plot(flag, name = "Tenth rise is big", style = histogram, color = color.green)
plot(newest, name = "Newest rise", color = color.blue)
plot(gains.size(), name = "Rises seen", display = none)

// A mistake on purpose: without the size test on the left, the tenth item is read before it exists.
indicator "Guarded read"
    edition = 1
    display = pane

state gains: array<float> = array<float>()
if close > close[1]
    gains.push(close - close[1])
let tenth_is_big = gains.at(9) > 2
let newest = if gains.size() > 0 then gains.last() else 0.0
let flag = if tenth_is_big then 1 else 0
plot(flag, name = "Tenth rise is big", style = histogram, color = color.green)
plot(newest, name = "Newest rise", color = color.blue)
plot(gains.size(), name = "Rises seen", display = none)

// `and`, `or`, `??` and the two arms of `if ... then ... else` run their right side only when it is needed.
// Pure operands (plain arithmetic, comparisons, values already bound to a name) are always fine there.
indicator "Lazy operators"
    edition = 1
    display = price

let average = tech.sma(close, 20)
let above = close > average
let near = math.abs(close - average) < tech.atr(14)
let signal = above and near
let fallback = average ?? close
plot(if signal then fallback else na, name = "Near and above", style = circles)

// Mistake: a call that keeps a state (tech.sma remembers its window) stands in the right side of `and`.
// That side runs only when the left side is true, so the window would move on some bars only. The checker refuses it (E3302).
indicator "Stateful call in an operand"
    edition = 1
    display = price

let rising = close > open
let strong = rising and close > tech.sma(close, 20)
plot(if strong then close else na, name = "Strong bars", style = circles)

indicator "Stateful call in an arm"
    edition = 1
    display = price

let fast = if close > open then tech.ema(close, 5) else na
plot(fast)

// The fix for E3302: bind the call to a name on its own line. It then runs on every bar and the window never skips one.
indicator "Stateful call bound first"
    edition = 1
    display = price

let average = tech.sma(close, 20)
let rising = close > open
let strong = rising and close > average
plot(if strong then close else na, name = "Strong bars", style = circles)

// Warning W3302: a call that keeps a state stands in an `if` block. It is allowed, but its state moves only on the bars where the block runs.
// Here the average of the up bars is smoothed over the up bars only, which is rarely what the line says.
indicator "Stateful call in a block"
    edition = 1
    display = price

mut smoothed: float = na
if close > open
    smoothed = tech.ema(close, 5)
plot(smoothed, name = "Smoothed")

// The fix for W3302: run the call on every bar above the block, and let the block only choose what to keep.
indicator "Stateful call above the block"
    edition = 1
    display = price

let smoothed_all = tech.ema(close, 5)
mut smoothed: float = na
if close > open
    smoothed = smoothed_all
plot(smoothed, name = "Smoothed")