/// <summary>
/// Applies beta reduction on invocation expressions in the given expression, using the specified configuration flags.
/// This is an advanced method which should be used with care when side-effects in expression trees are critical to maintain.
/// Some configurations may lead to changes in timing and the arity of side-effects.
/// </summary>
/// <param name="expression">Expression to apply beta reductions on.</param>
/// <param name="nodeTypes">Flags to restrict the argument expression node types that will be inlined during beta reduction. (Default: Atoms)</param>
/// <param name="restrictions">Flags to restrict the number of uses of each argument expression during inlining. (Default: None)</param>
/// <returns>Expression after applying beta reductions.</returns>
public static Expression Reduce(Expression expression, BetaReductionNodeTypes nodeTypes, BetaReductionRestrictions restrictions)
{
if (expression == null)
{
throw new ArgumentNullException(nameof(expression));
}
return(ReduceCore(expression, nodeTypes, restrictions));
}
public BetaReductionExpressionVisitor(BetaReductionNodeTypes nodeTypes, BetaReductionRestrictions restrictions)
{
_includeConstant = (nodeTypes & BetaReductionNodeTypes.Constant) != 0;
_includeDefault = (nodeTypes & BetaReductionNodeTypes.Default) != 0;
_includeParameter = (nodeTypes & BetaReductionNodeTypes.Parameter) != 0;
_includeQuote = (nodeTypes & BetaReductionNodeTypes.Quote) != 0;
_includeMolecules = (nodeTypes & BetaReductionNodeTypes.Molecules) != 0;
_inDangerOfCaptures = _includeParameter | _includeQuote | _includeMolecules;
_disallowDiscard = (restrictions & BetaReductionRestrictions.DisallowDiscard) != 0;
_disallowMultiple = (restrictions & BetaReductionRestrictions.DisallowMultiple) != 0;
}
/// <summary>
/// Applies beta reduction on invocation expressions in the given expression, using the specified configuration flags, until no further reductions are possible.
/// This is an advanced method which should be used with care when side-effects in expression trees are critical to maintain.
/// Some configurations may lead to changes in timing and the arity of side-effects.
/// </summary>
/// <param name="expression">Expression to apply beta reductions on.</param>
/// <param name="nodeTypes">Flags to restrict the argument expression node types that will be inlined during beta reduction.</param>
/// <param name="restrictions">Flags to restrict the number of uses of each argument expression during inlining.</param>
/// <param name="throwOnCycle">Indicates whether to throw an exception if the reduction gets stuck in a cyclic reduction (e.g. for a recursive lambda expression). If set to false, the reduction stops and the current expression is returned.</param>
/// <returns>Expression after applying beta reductions.</returns>
public static Expression ReduceEager(Expression expression, BetaReductionNodeTypes nodeTypes, BetaReductionRestrictions restrictions, bool throwOnCycle)
{
if (expression == null)
{
throw new ArgumentNullException(nameof(expression));
}
var history = new HashSet <Expression>(new ExpressionEqualityComparer());
var current = expression;
var reduced = default(Expression);
var i = 0;
while (current != reduced)
{
if (!history.Add(current))
{
if (throwOnCycle)
{
throw new InvalidOperationException(string.Format(CultureInfo.InvariantCulture, "Irreducible recursive lambda expression detected: '{0}'.", current));
}
else
{
break;
}
}
reduced = current;
current = ReduceCore(current, nodeTypes, restrictions);
i++;
}
return(current);
}
private static Expression ReduceCore(Expression expression, BetaReductionNodeTypes nodeTypes, BetaReductionRestrictions restrictions) => new BetaReductionExpressionVisitor(nodeTypes, restrictions).Visit(expression);