/// <summary>
/// Evaluate expression children and return them.
/// </summary>
/// <param name="expression">Expression with children.</param>
/// <param name="state">Global state.</param>
/// <param name="options">Options used in evaluation. </param>
/// <param name="verify">Optional function to verify each child's result.</param>
/// <returns>List of child values or error message.</returns>
public static (IReadOnlyList <object>, string error) EvaluateChildren(Expression expression, IMemory state, Options options, VerifyExpression verify = null)
{
var args = new List <object>();
object value;
string error = null;
var pos = 0;
foreach (var child in expression.Children)
{
(value, error) = child.TryEvaluate(state, options);
if (error != null)
{
break;
}
if (verify != null)
{
error = verify(value, child, pos);
}
if (error != null)
{
break;
}
args.Add(value);
++pos;
}
return(args, error);
}
// Apply -- these are helpers for adding functions to the expression library.
/// <summary>
/// Generate an expression delegate that applies function after verifying all children.
/// </summary>
/// <param name="function">Function to apply.</param>
/// <param name="verify">Function to check each arg for validity.</param>
/// <returns>Delegate for evaluating an expression.</returns>
public static EvaluateExpressionDelegate Apply(Func <IReadOnlyList <object>, object> function, VerifyExpression verify = null)
=>
(expression, state, options) =>
{
object value = null;
string error = null;
IReadOnlyList <object> args;
(args, error) = EvaluateChildren(expression, state, options, verify);
if (error == null)
{
try
{
value = function(args);
}
#pragma warning disable CA1031 // Do not catch general exception types (capture any exception and return it in the error)
catch (Exception e)
#pragma warning restore CA1031 // Do not catch general exception types
{
error = e.Message;
}
}
value = ResolveValue(value);
return(value, error);
};
// Apply -- these are helpers for adding functions to the expression library.
/// <summary>
/// Generate an expression delegate that applies function after verifying all children.
/// </summary>
/// <param name="function">Function to apply.</param>
/// <param name="verify">Function to check each arg for validity.</param>
/// <returns>Delegate for evaluating an expression.</returns>
public static EvaluateExpressionDelegate Apply(Func <IReadOnlyList <object>, object> function, VerifyExpression verify = null)
=>
(expression, state, options) =>
{
object value = null;
string error = null;
IReadOnlyList <object> args;
(args, error) = EvaluateChildren(expression, state, options, verify);
if (error == null)
{
try
{
value = function(args);
}
catch (Exception e)
{
error = e.Message;
}
}
value = ResolveValue(value);
return(value, error);
};
