# Lab Logic Toolkit

Lab Logic Toolkit (LLTK) provides the *evaluateDynamicExpression* script, which allows for the evaluation of simple dynamic expressions — Excel-like formulas that can be used to perform calculations. The expressions may include full Java or Groovy syntax.

Each Clarity LIMS step comprises a series of mappings that relate a single input to a single output. The script applies and evaluates the expression for each input-output-mapping in the step.

For example, the following expression sets the next step for each output sample, depending on whether the input sample has passed or failed QC:

{% code overflow="wrap" %}

```markup
-exp 'if (input.QC == true) { nextStep = ::ADVANCE:: } else { nextStep = ::ESCALATE:: }'
```

{% endcode %}

Often, the formulas are used to set the values of one or more custom fields. However, LLTK can do a great deal more than simply manipulate field values.


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