internal static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second, Func <Expression, Expression, Expression> merge)
{
// build parameter map (from parameters of second to parameters of first)
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
// replace parameters in the second lambda expression with parameters from
// the first
var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
// apply composition of lambda expression bodies to parameters from
// the first expression
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
/// <summary>
/// Combines the first expression with the second using the specified merge function.
/// </summary>
private static Expression <T> Compose <T>(
this Expression <T> first,
Expression <T> second,
Func <Expression, Expression, Expression> merge)
{
// Zip parameters (map from parameters of second to parameters of first)
Dictionary <ParameterExpression, ParameterExpression> map = first.Parameters
.Select((x, i) => new { f = x, s = second.Parameters[i] })
.ToDictionary(y => y.s, p => p.f);
// Replace parameters in the second lambda expression with the parameters in the first
Expression secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
// Create a merged lambda expression with parameters from the first expression
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
