Class Rewriter

Extension methods for IRewriter<T> implementations.

Inheritance

Object
Rewriter

Declaration

public static class Rewriter : Object

Methods

ChildrenInContext<T>(IRewriter<T>, T)

Returns an array containing each immediate child of value paired with a function to replace the child. This is typically useful when you need to replace a node's children one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the child; calling the function with a new child "plugs the hole" in the context.

SelfAndDescendantsInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)

Declaration

public static ValueTuple<T, Func<T, T>>[] ChildrenInContext<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to get the contexts for the immediate children

Returns

Type	Description
ValueTuple<T, Func<T, T>>[]

Type Parameters

Name	Description
T

Cursor<T>(IRewriter<T>, T)

Create a Cursor<T>(IRewriter<T>, T) focused on the root node of value.

Declaration

public static Cursor<T> Cursor<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The root node on which the newly created Cursor<T>(IRewriter<T>, T) should be focused

Returns

Type	Description
Cursor<T>	A Cursor<T>(IRewriter<T>, T) focused on the root node of `value`

Type Parameters

Name	Description
T

DescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, T)

Returns the descendant at a particular location in value

Declaration

public static T DescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
IEnumerable<Direction>	path	The route to take to find the descendant
T	value	The rewritable tree type

Returns

Type	Description
T	The descendant found by following the directions in `path`

Type Parameters

Name	Description
T

Exceptions

Type	Condition
InvalidOperationException	Thrown if `path` leads off the edge of the tree

DescendantsAndSelf<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value, starting at the bottom.

This is a depth-first post-order traversal.

SelfAndDescendants<T>(IRewriter<T>, T)

Declaration

public static IEnumerable<T> DescendantsAndSelf<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to traverse

Returns

Type	Description
IEnumerable<T>	An enumerable containing all of the nodes in the tree represented by `value`, starting at the bottom.

Type Parameters

Name	Description
T	The rewritable tree type

Examples

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);
Expr[] expected = new[]
    {
        new Lit(1),
        new Lit(2),
        new Add(new Lit(1), new Lit(2)),
        new Lit(3),
        expr    
    };
Assert.Equal(expected, rewriter.DescendantsAndSelf(expr));

DescendantsAndSelfInContext<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, starting at the bottom. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

This is a depth-first post-order traversal.

DescendantsAndSelf<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) SelfAndDescendantsInContext<T>(IRewriter<T>, T)

Declaration

public static IEnumerable<ValueTuple<T, Func<T, T>>> DescendantsAndSelfInContext<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to get the contexts for the descendants

Returns

Type	Description
IEnumerable<ValueTuple<T, Func<T, T>>>

Type Parameters

Name	Description
T

Fold<T, U>(IRewriter<T>, SpanFunc<U, T, U>, T)

Flattens all the nodes in the tree represented by value into a single result, using an aggregation function to combine each node with the results of folding its children.

Declaration

public static U Fold<T, U>(this IRewriter<T> rewriter, SpanFunc<U, T, U> func, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
SpanFunc<U, T, U>	func	The aggregation function
T	value	The value to fold

Returns

Type	Description
U	The result of aggregating the tree represented by `value`.

Type Parameters

Name	Description
T	The rewritable tree type
U	The type of the result of aggregation

Fold<T, U>(IRewriter<T>, Func<Memory, T, ValueTask>, T)

Flattens all the nodes in the tree represented by value into a single result, using an asynchronous aggregation function to combine each node with the results of folding its children.

Declaration

public static ValueTask<U> Fold<T, U>(this IRewriter<T> rewriter, Func<Memory<U>, T, ValueTask<U>> func, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<Memory<U>, T, ValueTask<U>>	func	The asynchronous aggregation function
T	value	The value to fold

Returns

Type	Description
ValueTask<U>	The result of aggregating the tree represented by `value`.

Type Parameters

Name	Description
T	The rewritable tree type
U	The type of the result of aggregation

Remarks

This method is not available on platforms which do not support ValueTask.

GetChildren<T>(IRewriter<T>, T)

Get the immediate children of the value. GetChildren(Span<T>)

Declaration

public static T[] GetChildren<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value

Returns

Type	Description
T[]	The immediate children of `value`

Type Parameters

Name	Description
T	The rewritable tree type

Examples

Given a representation of the expression (1+2)+3,

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);

GetChildren<T>(IRewriter<T>, T) returns the immediate children of the topmost node.

Expr[] expected = new[]
    {
        new Add(
            new Lit(1),
            new Lit(2)
        ),
        new Lit(3)
    };
Assert.Equal(expected, rewriter.GetChildren(expr));

ReplaceDescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, T, T)

Replaces the descendant at a particular location in value

Declaration

public static T ReplaceDescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, T newDescendant, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
IEnumerable<Direction>	path	The route to take to find the descendant
T	newDescendant	The replacement descendant
T	value	The rewritable tree type

Returns

Type	Description
T	A copy of `value` with `newDescendant` placed at the location indicated by `path`

Type Parameters

Name	Description
T

Exceptions

Type	Condition
InvalidOperationException	Thrown if `path` leads off the edge of the tree

Rewrite<T>(IRewriter<T>, Func<T, T>, T)

Rebuild a tree by applying a transformation function to every node from bottom to top.

Declaration

public static T Rewrite<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, T>	transformer	The transformation function to apply to every node in the tree
T	value	The value to rewrite

Returns

Type	Description
T	The result of applying `transformer` to every node in the tree represented by `value`.

Type Parameters

Name	Description
T	The rewritable tree type

Examples

Given a representation of the expression (1+2)+3,

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);

Rewrite<T>(IRewriter<T>, Func<T, T>, T) replaces the leaves of the tree with the result of calling transformer, then replaces their parents with the result of calling transformer, and so on. By the end, Rewrite<T>(IRewriter<T>, Func<T, T>, T) has traversed the whole tree.

Expr expected = transformer(new Add(
    transformer(new Add(
        transformer(new Lit(1)),
        transformer(new Lit(2))
    )),
    transformer(new Lit(3))
));
Assert.Equal(expected, rewriter.Rewrite(transformer, expr));

Rewrite<T>(IRewriter<T>, Func<T, ValueTask<T>>, T)

Rebuild a tree by applying an asynchronous transformation function to every node from bottom to top.

Declaration

public static ValueTask<T> Rewrite<T>(this IRewriter<T> rewriter, Func<T, ValueTask<T>> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, ValueTask<T>>	transformer	The asynchronous transformation function to apply to every node in the tree
T	value	The value to rewrite

Returns

Type	Description
ValueTask<T>	The result of applying `transformer` to every node in the tree represented by `value`.

Type Parameters

Name	Description
T	The rewritable tree type

Remarks

This method is not available on platforms which do not support ValueTask.

Examples

Given a representation of the expression (1+2)+3,

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);

Rewrite<T>(IRewriter<T>, Func<T, ValueTask<T>>, T) replaces the leaves of the tree with the result of calling transformer, then replaces their parents with the result of calling transformer, and so on. By the end, Rewrite<T>(IRewriter<T>, Func<T, ValueTask<T>>, T) has traversed the whole tree.

Expr expected = await transformer(new Add(
    await transformer(new Add(
        await transformer(new Lit(1)),
        await transformer(new Lit(2))
    )),
    await transformer(new Lit(3))
));
Assert.Equal(expected, await rewriter.Rewrite(transformer, expr));

RewriteChildren<T>(IRewriter<T>, Func<T, T>, T)

Update the immediate children of the value by applying a transformation function to each one.

Declaration

public static T RewriteChildren<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, T>	transformer	A transformation function to apply to each of `value`'s immediate children.
T	value	The old value, whose immediate children should be transformed by `transformer`.

Returns

Type	Description
T	A copy of `value` with updated children.

Type Parameters

Name	Description
T	The rewritable tree type

RewriteChildren<T>(IRewriter<T>, Func<T, ValueTask<T>>, T)

Update the immediate children of the value by applying an asynchronous transformation function to each one.

Declaration

public static ValueTask<T> RewriteChildren<T>(this IRewriter<T> rewriter, Func<T, ValueTask<T>> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, ValueTask<T>>	transformer	An asynchronous transformation function to apply to each of `value`'s immediate children.
T	value	The old value, whose immediate children should be transformed by `transformer`.

Returns

Type	Description
ValueTask<T>	A copy of `value` with updated children.

Type Parameters

Name	Description
T	The rewritable tree type

Remarks

This method is not available on platforms which do not support ValueTask.

RewriteDescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, Func<T, T>, T)

Apply a function at a particular location in value

Declaration

public static T RewriteDescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, Func<T, T> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
IEnumerable<Direction>	path	The route to take to find the descendant
Func<T, T>	transformer	A function to calculate a replacement for the descendant
T	value	The rewritable tree type

Returns

Type	Description
T	A copy of `value` with the result of `transformer` placed at the location indicated by `path`

Type Parameters

Name	Description
T

Exceptions

Type	Condition
InvalidOperationException	Thrown if `path` leads off the edge of the tree

RewriteDescendantAt<T>(IRewriter<T>, IEnumerable<Direction>, Func<T, ValueTask<T>>, T)

Apply an asynchronous function at a particular location in value

Declaration

public static ValueTask<T> RewriteDescendantAt<T>(this IRewriter<T> rewriter, IEnumerable<Direction> path, Func<T, ValueTask<T>> transformer, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
IEnumerable<Direction>	path	The route to take to find the descendant
Func<T, ValueTask<T>>	transformer	An asynchronous function to calculate a replacement for the descendant
T	value	The rewritable tree type

Returns

Type	Description
ValueTask<T>	A copy of `value` with the result of `transformer` placed at the location indicated by `path`

Type Parameters

Name	Description
T

Remarks

This method is not available on platforms which do not support ValueTask.

Exceptions

Type	Condition
InvalidOperationException	Thrown if `path` leads off the edge of the tree

RewriteIter<T>(IRewriter<T>, Func<T, T>, T)

Rebuild a tree by repeatedly applying a transformation function to every node in the tree, until a fixed point is reached. transformer should always eventually return its argument unchanged, or this method will loop. That is, x.RewriteIter(transformer).SelfAndDescendants().All(x => transformer(x) == x).

This is typically useful when you want to put your tree into a normal form by applying a collection of rewrite rules until none of them can fire any more.

Declaration

public static T RewriteIter<T>(this IRewriter<T> rewriter, Func<T, T> transformer, T value)
    where T : class

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, T>	transformer	A transformation function to apply to every node in `value` repeatedly.
T	value	The value to rewrite

Returns

Type	Description
T	The result of applying `transformer` to every node in the tree represented by `value` repeatedly until a fixed point is reached.

Type Parameters

Name	Description
T	The rewritable tree type

RewriteIter<T>(IRewriter<T>, Func<T, ValueTask<T>>, T)

Rebuild a tree by repeatedly applying an asynchronous transformation function to every node in the tree, until a fixed point is reached. transformer should always eventually return its argument unchanged, or this method will loop. That is, x.RewriteIter(transformer).SelfAndDescendants().All(x => await transformer(x) == x).

This is typically useful when you want to put your tree into a normal form by applying a collection of rewrite rules until none of them can fire any more.

Declaration

public static ValueTask<T> RewriteIter<T>(this IRewriter<T> rewriter, Func<T, ValueTask<T>> transformer, T value)
    where T : class

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T, ValueTask<T>>	transformer	An asynchronous transformation function to apply to every node in `value` repeatedly.
T	value	The value to rewrite

Returns

Type	Description
ValueTask<T>	The result of applying `transformer` to every node in the tree represented by `value` repeatedly until a fixed point is reached.

Type Parameters

Name	Description
T	The rewritable tree type

Remarks

This method is not available on platforms which do not support ValueTask.

SelfAndDescendants<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value, starting at the top.

This is a depth-first pre-order traversal.

DescendantsAndSelf<T>(IRewriter<T>, T)

Declaration

public static IEnumerable<T> SelfAndDescendants<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to traverse

Returns

Type	Description
IEnumerable<T>	An enumerable containing all of the nodes in the tree represented by `value`, starting at the top.

Type Parameters

Name	Description
T	The rewritable tree type

Examples

Expr expr = new Add(
    new Add(
        new Lit(1),
        new Lit(2)
    ),
    new Lit(3)
);
Expr[] expected = new[]
    {
        expr,
        new Add(new Lit(1), new Lit(2)),
        new Lit(1),
        new Lit(2),
        new Lit(3),
    };
Assert.Equal(expected, rewriter.SelfAndDescendants(expr));

SelfAndDescendantsBreadthFirst<T>(IRewriter<T>, T)

Yields all of the nodes in the tree represented by value in a breadth-first traversal order.

This is a breadth-first pre-order traversal.

Declaration

public static IEnumerable<T> SelfAndDescendantsBreadthFirst<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to traverse

Returns

Type	Description
IEnumerable<T>	An enumerable containing all of the nodes in the tree represented by `value` in a breadth-first traversal order.

Type Parameters

Name	Description
T	The rewritable tree type

SelfAndDescendantsInContext<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, starting at the top. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

This is a depth-first pre-order traversal.

SelfAndDescendants<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)

Declaration

public static IEnumerable<ValueTuple<T, Func<T, T>>> SelfAndDescendantsInContext<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to get the contexts for the descendants

Returns

Type	Description
IEnumerable<ValueTuple<T, Func<T, T>>>

Type Parameters

Name	Description
T

SelfAndDescendantsInContextBreadthFirst<T>(IRewriter<T>, T)

Yields each node in the tree represented by value paired with a function to replace the node, in a breadth-first traversal order. This is typically useful when you need to replace nodes one at a time, such as during mutation testing.

The replacement function can be seen as the "context" of the node; calling the function with a new node "plugs the hole" in the context.

This is a breadth-first pre-order traversal.

SelfAndDescendants<T>(IRewriter<T>, T) ChildrenInContext<T>(IRewriter<T>, T) DescendantsAndSelfInContext<T>(IRewriter<T>, T)

Declaration

public static IEnumerable<ValueTuple<T, Func<T, T>>> SelfAndDescendantsInContextBreadthFirst<T>(this IRewriter<T> rewriter, T value)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
T	value	The value to get the contexts for the descendants

Returns

Type	Description
IEnumerable<ValueTuple<T, Func<T, T>>>

Type Parameters

Name	Description
T

ZipFold<T, U>(IRewriter<T>, Func<T[], IAsyncEnumerable, ValueTask>, T[])

Flatten all of the nodes in the trees represented by values into a single value at the same time, using an aggregation function to combine nodes with the results of aggregating their children. The trees are iterated in lock-step, much like an n-ary Zip<TFirst,TSecond,TResult>(IEnumerable<TFirst>, IEnumerable<TSecond>, Func<TFirst,TSecond,TResult>).

When trees are not the same size, the larger ones are truncated both horizontally and vertically. That is, if a pair of nodes have a different number of children, the rightmost children of the larger of the two nodes are discarded.

Declaration

public static ValueTask<U> ZipFold<T, U>(this IRewriter<T> rewriter, Func<T[], IAsyncEnumerable<U>, ValueTask<U>> func, params T[] values)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T[], IAsyncEnumerable<U>, ValueTask<U>>	func	The aggregation function
T[]	values	The trees to fold

Returns

Type	Description
ValueTask<U>	The result of aggregating the two trees

Type Parameters

Name	Description
T	The rewritable tree type
U	The return type of the aggregation

Remarks

This method is not available on platforms which do not support ValueTask and IAsyncEnumerable<T>.

Examples

Here's an example of using ZipFold<T, U>(IRewriter<T>, Func<T[], IAsyncEnumerable, ValueTask>, T[]) to test if two trees are syntactically equal.

static bool Equals(this Expr left, Expr right)
    => left.ZipFold<Expr, bool>(
        right,
        (xs, results) =>
        {
            switch (xs[0])
            {
                case Add a1 when xs[1] is Add a2:
                    return results.All(x => x);
                case Lit l1 when xs[1] is Lit l2:
                    return l1.Value == l2.Value;
                default:
                    return false;
            }
        }
    );

ZipFold<T, U>(IRewriter<T>, Func<T[], IEnumerable, U>, T[])

Declaration

public static U ZipFold<T, U>(this IRewriter<T> rewriter, Func<T[], IEnumerable<U>, U> func, params T[] values)

Parameters

Type	Name	Description
IRewriter<T>	rewriter	The rewriter
Func<T[], IEnumerable<U>, U>	func	The aggregation function
T[]	values	The trees to fold

Returns

Type	Description
U	The result of aggregating the two trees

Type Parameters

Name	Description
T	The rewritable tree type
U	The return type of the aggregation

Examples

Here's an example of using ZipFold<T, U>(IRewriter<T>, Func<T[], IEnumerable, U>, T[]) to test if two trees are syntactically equal.

static bool Equals(this Expr left, Expr right)
    => left.ZipFold<Expr, bool>(
        right,
        (xs, results) =>
        {
            switch (xs[0])
            {
                case Add a1 when xs[1] is Add a2:
                    return results.All(x => x);
                case Lit l1 when xs[1] is Lit l2:
                    return l1.Value == l2.Value;
                default:
                    return false;
            }
        }
    );