{:eval; ... :}
==============
Output code if the result of eval is not empty (non-zero length).
```html
{:eval; code >> code :}
{:eval; {:;varname:} >>
shown if varname is not empty
:}
```
A variable is set with the result of the evaluation:
```html
{:eval; {:;varname:} >>
...
{:;__eval__:}
...
:}
```
Modifiers:
----------
```html
{:!eval; ... :}
{:+eval; ... :}
{:^eval; ... :}
```
For more details about the "+" modifier see "modifiers".
### Modifier: ! (not)
```html
{:!eval; {:;varname:} >>
shown if varname is empty
:}
```
No flags
--------
Usage
-----
Eval evaluates code versus filled which evaluates a variable:
```html
{:filled; varname >>
...
:}
{:eval; {:code: {:;varname:} :} >>
...
:}
```
Sometimes it is necessary to evaluate code:
```html
<li>{:snippet; snippet-name :}</li>
```
The output of the above if "snippet-name" is empty will be:
```html
<li></li>
```
To prevent this from happening, it can be done:
```html
{:eval; {:snippet; snippet-name :} >>
<li>{:;__eval__:}</li>
:}
```
And in this case the "li" will only be displayed if "snippet-name" is not empty.
The following are equivalent, but the first does not require re-evaluation of the snippet and may be clearer as to what is intended:
```html
{:eval; {:snippet; snippet-name :} >>
<li>{:;__eval__:}</li>
:}
```
```html
{:eval; {:snippet; snippet-name :} >>
<li>{:snippet; snippet-name :}</li>
:}
```
This is also possible
```html
{:eval; {:;varname1:}{:;varname2:} >>
...
{:;__eval__:}
...
:}
```
```html
{:eval;
{:code;
... a lot of code here ...
:}
>>
...
{:;__eval__:}
...
:}
```
Can also be used to prevent output, in the following example, we want the include to show a possible output:
```html
{:+eval; {:include; file :} >> :}
```
For more details about the "+" modifier see "modifiers".
---
