# MQTT Engine (SimpleTagProvider) Unknown function: 'concat'

**URL:** <https://forum.inductiveautomation.com/t/mqtt-engine-simpletagprovider-unknown-function-concat/18750>\
**Category:** Ignition\
**Created:** [July 6, 2018, 9:13am UTC](https://forum.inductiveautomation.com/t/mqtt-engine-simpletagprovider-unknown-function-concat/18750 "2018-07-06T09:13:51Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Amarth](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/amarth/32/3313_2.png) [@Amarth](https://forum.inductiveautomation.com/u/Amarth)\
**Post date:** [July 6, 2018, 9:13am UTC](https://forum.inductiveautomation.com/t/mqtt-engine-simpletagprovider-unknown-function-concat/18750/1 "2018-07-06T09:13:51Z")

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Hello all,

I have a strange behavior of the evaluation of an expression. The expression is a simple concat of three strings that works perfectly.

As soon as it is evaluated in a simpleTagProvider (The MQTT Engine Tag Provider) I got the following error : Unknown function: ‘concat’.

Note that the workaroud of summing the string works, but I would really prefer to use the concat expression.

Is it a normal behavior ?

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<div class="post-metadata">

**Author:** ![Amarth](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/amarth/32/3313_2.png) [@Amarth](https://forum.inductiveautomation.com/u/Amarth)\
**Post date:** [July 6, 2018, 9:38am UTC](https://forum.inductiveautomation.com/t/mqtt-engine-simpletagprovider-unknown-function-concat/18750/2 "2018-07-06T09:38:45Z")

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Something more stange:  
When I bind a property to a member of the same UDT, when evaluated, the bind is in error, telling that the member can not be located.

 ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/a/a4ca01f55991aad18ea032c475433ffc586b5aa7.png)  
 ![](https://us1.discourse-cdn.com/inductiveautomation/original/2X/0/04294c8ba2bc1658ea601422b9736bc0604e3fe2.png)

The exact same binding works perfectly on a “normal” tagProvider.