Cannot use Linq expression

[ymeric]

When I use a Linq expression like the example below, I'm getting the error message below. I am adding the Linq enumerable class to the expression context using context.Imports.AddType(typeof(Enumerable)); but it doesn't help. What am I missing?

Error Message:

Flee.PublicTypes.ExpressionCompileException: 'IdentifierElement: Could not find a field/property/variable with the name 'p''

Linq Expression:

SomeParameter.Select(p=>p.substring(0, p.indexOf("|"))).ToList())

SomeParameter is a string array.