closure-builder/third_party/closure-templates/documentation/concepts/expressions.md

Simple Closure, Soy and JavaScript Build system

# Expressions

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## What are `Closure Templates` expressions?

Expressions are another high level `Closure Templates` concept. They are written
within templates to reference template data, variables, or compute intermediate
values.

## What types of expressions are there?

TIP: For a complete list, see the [reference section](../reference/index).

### Literals

Literals are just that: literal expressions of values like integers (`100`,
`0x64`) or booleans (`true`, `false`). The `Closure Templates` compiler evaluates
them as they are.

### Variables

Variables are things like parameters (`$myParam`), globals, and injected data.

### Operators

Mathematical operators like `+`, or `>`, and data access operators for protos,
among others.

NOTE: In `Closure Templates`, operators follow a strict [order of
precedence](../reference/expressions.md#precedence).

### Function calls

More about this in the next concepts section.

## Where are expressions used?

`Closure Templates` uses a language-neutral expression syntax, and expressions show
up in lots of different places in `Closure Templates`. The most common place is in
print commands, but they are also used in [if
commands](../reference/control-flow.md#if), [let
declarations](../reference/let.md), and many other places.

For example:

```soy
{template .myTemplate}
  {@param p: ?}
  {if $p > 2}
    {call .bar}{param p : $p == 3 ? 'a' : 'b' /}{/call}
  {/if}
{/template}
```

In the above example, we can see a parameter `p` being used in several
expressions for several different commands.

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