Expressions, declarations and statements

Expressions

An expression is a sequence of applying both operators and function calls to operands (variables, values), which determines the calculations and actions done by the script. Expressions in Pine almost always produce a result (exceptions are the functions study, fill, strategy.entry, etc. They produce side effects and will be covered later).

Here are some examples of simple expressions:

(high + low + close)/3
sma(high - low, 10) + sma(close, 20)

Variable declaration

Variables in Pine are declared with the help of the special symbol = in the following way:

<identifier> = <expression>

In place of <identifier> will be the name of the declared variable. Examples of Variable Declarations:

src = close
len = 10
ma = sma(src, len) + high

Three variables were declared here: src, len and ma. Identifiers close and high are built-in variables. The identifier sma is a built-in function for calculating Simple Moving Average.

Variable assignment

Mutable variable is such a variable which can be given a new value.

The operator := must be used to give a new value to a variable. To use this operator, a special attribute must be used in the first line of a code: //@version=2. This attribute identifies the version of Pine Script. Mutable variables were introduced in version 2.

A variable must be declared before you can set a value for it (declaration of variables has been described above).

Type of a variable is identified on the declaration step. A variable can be given a value of expression only if both the expression and the variable belong to the same type, otherwise it will give you a compilation error.

Variable assignment example:

//@version=2
study("My Script")
price = close
if hl2 > price
    price := hl2
plot(price)

We also use an “if” statement in this example.

Self referencing variables

The ability to reference the previous values of declared variables in expressions where they are declared (using the operator []) is a useful feature in Pine. These variables are called self referencing variables. For Example:

//@version=2
study("Fibonacci numbers")
fib = na(fib[1]) or na(fib[2]) ? 1 : fib[1] + fib[2]
plot(fib)

Note

self referencing variables and forward referencing variables were removed in version 3.

In Pine version 3, this can be achieved using the syntax of mutable variables:

//@version=3
study("Fibonacci numbers v3")
fib = 0
fib := na(fib[1]) or na(fib[2]) ? 1 : fib[1] + fib[2]
plot(fib)

See also Pine version 3 migration guide.

Expert tip: mod out the Fibonacci numbers by 1000 to generate a plot you can actually see:

//@version=3
study("Fibonacci numbers v3")
fib = 0
fib := (na(fib[1]) or na(fib[2]) ? 1 : fib[1] + fib[2]) % 1000
plot(fib)

The variable fib is a series of Fibonacci numbers : 1, 1, 2, 3, 5, 8, 13, 21, …, where the first two numbers are equal to 1 and 1 and each subsequent number is the sum of the last two. In the given example, the built-in function na is used and returns true if the value of its argument has still not been determined (is na). In the example produced below, the values fib[1] and fib[2] have not been determined on the first bar, while on the second bar fib[2] has not been determined. Finally, on the third bar both of them are defined and can be added. images/Fib.png

Note

Since the sequence of Fibonacci numbers grows rather fast, the variable fib very quickly overflows. As such, the user should apply the given indicator on the monthly “M” or yearly “Y” resolution, otherwise the value “n/a” will be on the chart instead of the Fibonacci numbers.

Preventing na values, functions na and nz

Self referencing variables allow for the accumulation of values during the indicator’s calculation on the bars. However there is one point to remember. For example, let’s assume we want to count all the bars on the chart with the following script:

barNum = barNum[1] + 1

The self referencing variable barNum refers to its own value on the previous bar, meaning, when the indicator will be calculated on every bar, the value barNum[1] will be equal to na. Therefore, on the first bar barNum[1] has no value. Adding 1 to na will still produce the na as a result. In total, the entire barNum series will be equal on every bar to na.

In order to avoid similar problems, Pine has a built-in function nz. This function takes an argument and if it is equal to na then it returns 0, otherwise it returns the argument’s value. Afterwards, the problem with the bars’ calculation is solved in the following way:

barNum = nz(barNum[1]) + 1

There is an overloaded version of nz with two arguments which returns the second argument if the first is equal to na. Further information about nz can be found here.

In addition, there is a simple function with one argument that returns a logical result called na. This function makes it possible to check if the argument is na or not. Check it out here.

The difference between na and nz: na returns a boolean value (true or false), and is therefore useful in constructing logical expressions (e.g., if na(x)). nz is a “filler”, as it fills na values of a series with zeros (in the case of nz(x)) or with a user-specified value (in the case of nz(x, y)). Note: the double-argument version nz(x, y) is equivalent to the logical construction na(x) ? y : x. (?: is a ternary operator).

Simple moving average without applying the function sma

While using self referencing variables, it’s possible to write the equivalent of the built-in function sma which calculates the simple moving average (SMA):

study("Pine Script SMA", overlay=true)
src = close
len = 9
sum = nz(sum[1]) - nz(src[len]) + src
plot(sum/len)

The variable sum is a moving sum with one window that has a length len. On each bar the variable sum is equal to its previous value, then the leftmost value in a moving window is subtracted from sum and a new value, which entered the moving window (the rightmost), is added. This is the algorithm optimized for vector languages, see Moving Average for a detailed basic algorithm description.

Further, before the graph is rendered, the sum is divided by the window size len and the indicator is displayed on the chart.

if statement

if statement defines what block of statements must be executed when conditions of the expression are satisfied.

To have access to and use the if statement, one should specify the version of Pine Script language in the very first line of code: //@version=2

General code form:

<var_declarationX> = if <condition>
    <var_decl_then0>
    <var_decl_then1>
    ...
    <var_decl_thenN>
    <return_expression_then>
else
    <var_decl_else0>
    <var_decl_else1>
    ...
    <var_decl_elseN>
    <return_expression_else>

where:

  • var_declarationX — this variable gets the value of the if statement.
  • condition — if the condition expression is true, the logic from the then block (var_decl_then0, var_decl_then1, etc.) is used, if the condition is false, the logic from the else block (var_decl_else0, var_decl_else1, etc.) is used.
  • return_expression_then, return_expression_else — the last expression from the then block or from the else block will return the final value of the whole if statement. If declaration of the variable is in the end, its value will be the result.

The type of returning value of the if statement depends on return_expression_then and return_expression_else type (their types must match, it is not possible to return an integer value from the then block, while you have a string value in the else block).

Example:

// This code compiles
x = if close > open
    close
else
    open
// This code doesn't compile
x = if close > open
    close
else
    "open"

It is possible to omit the else block. In this case, if the condition is false, an empty value (na, or false, or "") will be assigned to the var_declarationX variable.

Example:

x = if close > open
    close
// If current close > current open, then x = close.
// Otherwise the x = na.

The blocks then and else are shifted by 4 spaces [1]. If statements can be nested, then add 4 more spaces:

x = if close > open
    b = if close > close[1]
        close
    else
        close[1]
    b
else
    open

It is possible to ignore the resulting value of an if statement (var_declarationX = can be omited). It may be useful if you need the side effect of the expression, for example in strategy trading:

if (crossover(source, lower))
    strategy.entry("BBandLE", strategy.long, stop=lower,
                   oca_name="BollingerBands",
                   oca_type=strategy.oca.cancel, comment="BBandLE")
else
    strategy.cancel(id="BBandLE")

for statement

for statement allows to execute a number of instructions repeatedly. To use for statements, a special attribute must be used in the first line of a code: //@version=2. This attribute identifies the version of Pine Script. for statements were introduced in version 2.

General code form:

<var_declarationX> = for <i> = <from> to <to> by <step>
    <var_decl0>
    <var_decl1>
    ...
    continue
    ...
    break
    ...
    <var_declN>
    <return_expression>

where:

  • i — a loop counter variable.
  • from — start value of the counter.
  • to — end value of the counter. When the counter becomes greater than to (or less than to in case from > to) the loop is stopped.
  • step — loop step. Can be omitted (by default loop step = 1). If from is greater than to loop step will change direction automatically, no need to specify negative numbers.
  • var_decl0, … var_declN, return_expression — body of the loop. It must be shifted by 4 spaces [1].
  • return_expression — returning value. When a loop is finished or broken, the returning value is given to the var_declarationX.
  • continue — a keyword. Can be used only in loops. It switches the loop to the next iteration.
  • break — a keyword. Can be used only in loops. It breaks (stops) the loop.

for loop example:

//@version=2
study("For loop")
my_sma(price, length) =>
    sum = price
    for i = 1 to length-1
        sum := sum + price[i]
    sum / length
plot(my_sma(close,14))

Variable sum is a mutable variable and a new value can be given to it by the operator := in body of the loop. Also note that we recommend to use a built-in function sma for simple moving average as it calculates faster.

Note that some built-in functions may behave unexpectedly in for loop. Let’s look at the following example:

//@version=3
study("RMA in for loop")
sum = 0.0
for i = 1 to 2
    sum := sum + rma(close, i)
plot(sum)

While you may expect that sum will contain rma(close, 1) + rma(close, 2), this is not so. It will contain rma(close, 1) + rma(close, 1) because once rma is initialized with length 1, this length is stored until the script is removed from chart. To avoid this you may use your own, stateless function implementation. There is the list of built-in functions which have the same behavior:

  • rma(source, length): length is stateful.
  • ema(source, length): length is stateful.
  • valuewhen(condition, source, occurrence): occurrence is stateful.
  • rsi(x, y): when y is of type integer and behaves like a length, y is stateful.

Footnotes

[1](1, 2) On TradingView Pine Editor the Tab key produces 4 spaces automatically.
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