page for transformer_and_visitor

docs/classes.md

@@ -94,119 +94,6 @@ Trees can be hashed and compared.
 
 ## Transformers & Visitors
 
-Transformers & Visitors provide a convenient interface to process the parse-trees that Lark returns.
-
-They are used by inheriting from the correct class (visitor or transformer), and implementing methods corresponding to the rule you wish to process. Each methods accepts the children as an argument. That can be modified using the `v_args` decorator, which allows to inline the arguments (akin to `*args`), or add the tree `meta` property as an argument.
-
-See: https://github.com/lark-parser/lark/blob/master/lark/visitors.py
-
-### Visitors
-
-Visitors visit each node of the tree, and run the appropriate method on it according to the node's data.
-
-They work bottom-up, starting with the leaves and ending at the root of the tree.
-
-**Example**
-```python
-class IncreaseAllNumbers(Visitor):
-  def number(self, tree):
-    assert tree.data == "number"
-    tree.children[0] += 1
-
-IncreaseAllNumbers().visit(parse_tree)
-```
-
-There are two classes that implement the visitor interface:
-
-* Visitor - Visit every node (without recursion)
-
-* Visitor_Recursive - Visit every node using recursion. Slightly faster.
-
-### Transformers
-
-Transformers visit each node of the tree, and run the appropriate method on it according to the node's data.
-
-They work bottom-up (or: depth-first), starting with the leaves and ending at the root of the tree.
-
-Transformers can be used to implement map & reduce patterns.
-
-Because nodes are reduced from leaf to root, at any point the callbacks may assume the children have already been transformed (if applicable).
-
-Transformers can be chained into a new transformer by using multiplication.
-
-**Example:**
-```python
-from lark import Tree, Transformer
-
-class EvalExpressions(Transformer):
-    def expr(self, args):
-            return eval(args[0])
-
-t = Tree('a', [Tree('expr', ['1+2'])])
-print(EvalExpressions().transform( t ))
-
-# Prints: Tree(a, [3])
-```
-
-
-Here are the classes that implement the transformer interface:
-
-- Transformer - Recursively transforms the tree. This is the one you probably want.
-- Transformer_InPlace - Non-recursive. Changes the tree in-place instead of returning new instances
-- Transformer_InPlaceRecursive - Recursive. Changes the tree in-place instead of returning new instances
-
-### v_args
-
-`v_args` is a decorator.
-
-By default, callback methods of transformers/visitors accept one argument: a list of the node's children. `v_args` can modify this behavior.
-
-When used on a transformer/visitor class definition, it applies to all the callback methods inside it.
-
-`v_args` accepts one of three flags:
-
-- `inline` - Children are provided as `*args` instead of a list argument (not recommended for very long lists).
-- `meta` - Provides two arguments: `children` and `meta` (instead of just the first)
-- `tree` - Provides the entire tree as the argument, instead of the children.
-
-Examples:
-
-```python
-@v_args(inline=True)
-class SolveArith(Transformer):
-    def add(self, left, right):
-        return left + right
-
-
-class ReverseNotation(Transformer_InPlace):
-    @v_args(tree=True):
-    def tree_node(self, tree):
-        tree.children = tree.children[::-1]
-```
-
-### Discard
-
-When raising the `Discard` exception in a transformer callback, that node is discarded and won't appear in the parent.
-
-## Token
-
-When using a lexer, the resulting tokens in the trees will be of the Token class, which inherits from Python's string. So, normal string comparisons and operations will work as expected. Tokens also have other useful attributes:
-
-* `type` - Name of the token (as specified in grammar).
-* `pos_in_stream` - the index of the token in the text
-* `line` - The line of the token in the text (starting with 1)
-* `column` - The column of the token in the text (starting with 1)
-* `end_line` - The line where the token ends
-* `end_column` - The next column after the end of the token. For example, if the token is a single character with a `column` value of 4, `end_column` will be 5.
-
-
-## UnexpectedInput
-
-- `UnexpectedInput`
-    - `UnexpectedToken` - The parser recieved an unexpected token
-    - `UnexpectedCharacters` - The lexer encountered an unexpected string
-
-After catching one of these exceptions, you may call the following helper methods to create a nicer error message:
 
 ### Methods
 

docs/transfromer_and_vistor.md

@@ -0,0 +1,115 @@
+## Transformers & Visitors
+
+Transformers & Visitors provide a convenient interface to process the parse-trees that Lark returns.
+
+They are used by inheriting from the correct class (visitor or transformer), and implementing methods corresponding to the rule you wish to process. Each methods accepts the children as an argument. That can be modified using the `v_args` decorator, which allows to inline the arguments (akin to `*args`), or add the tree `meta` property as an argument.
+
+See: https://github.com/lark-parser/lark/blob/master/lark/visitors.py
+
+### Visitors
+
+Visitors visit each node of the tree, and run the appropriate method on it according to the node's data.
+
+They work bottom-up, starting with the leaves and ending at the root of the tree.
+
+**Example**
+```python
+class IncreaseAllNumbers(Visitor):
+  def number(self, tree):
+    assert tree.data == "number"
+    tree.children[0] += 1
+
+IncreaseAllNumbers().visit(parse_tree)
+```
+
+There are two classes that implement the visitor interface:
+
+* Visitor - Visit every node (without recursion)
+
+* Visitor_Recursive - Visit every node using recursion. Slightly faster.
+
+### Transformers
+
+Transformers visit each node of the tree, and run the appropriate method on it according to the node's data.
+
+They work bottom-up (or: depth-first), starting with the leaves and ending at the root of the tree.
+
+Transformers can be used to implement map & reduce patterns.
+
+Because nodes are reduced from leaf to root, at any point the callbacks may assume the children have already been transformed (if applicable).
+
+Transformers can be chained into a new transformer by using multiplication.
+
+**Example:**
+```python
+from lark import Tree, Transformer
+
+class EvalExpressions(Transformer):
+    def expr(self, args):
+            return eval(args[0])
+
+t = Tree('a', [Tree('expr', ['1+2'])])
+print(EvalExpressions().transform( t ))
+
+# Prints: Tree(a, [3])
+```
+
+
+Here are the classes that implement the transformer interface:
+
+- Transformer - Recursively transforms the tree. This is the one you probably want.
+- Transformer_InPlace - Non-recursive. Changes the tree in-place instead of returning new instances
+- Transformer_InPlaceRecursive - Recursive. Changes the tree in-place instead of returning new instances
+
+### v_args
+
+`v_args` is a decorator.
+
+By default, callback methods of transformers/visitors accept one argument: a list of the node's children. `v_args` can modify this behavior.
+
+When used on a transformer/visitor class definition, it applies to all the callback methods inside it.
+
+`v_args` accepts one of three flags:
+
+- `inline` - Children are provided as `*args` instead of a list argument (not recommended for very long lists).
+- `meta` - Provides two arguments: `children` and `meta` (instead of just the first)
+- `tree` - Provides the entire tree as the argument, instead of the children.
+
+Examples:
+
+```python
+@v_args(inline=True)
+class SolveArith(Transformer):
+    def add(self, left, right):
+        return left + right
+
+
+class ReverseNotation(Transformer_InPlace):
+    @v_args(tree=True):
+    def tree_node(self, tree):
+        tree.children = tree.children[::-1]
+```
+
+### Discard
+
+When raising the `Discard` exception in a transformer callback, that node is discarded and won't appear in the parent.
+
+## Token
+
+When using a lexer, the resulting tokens in the trees will be of the Token class, which inherits from Python's string. So, normal string comparisons and operations will work as expected. Tokens also have other useful attributes:
+
+* `type` - Name of the token (as specified in grammar).
+* `pos_in_stream` - the index of the token in the text
+* `line` - The line of the token in the text (starting with 1)
+* `column` - The column of the token in the text (starting with 1)
+* `end_line` - The line where the token ends
+* `end_column` - The next column after the end of the token. For example, if the token is a single character with a `column` value of 4, `end_column` will be 5.
+
+
+## UnexpectedInput
+
+- `UnexpectedInput`
+    - `UnexpectedToken` - The parser recieved an unexpected token
+    - `UnexpectedCharacters` - The lexer encountered an unexpected string
+
+After catching one of these exceptions, you may call the following helper methods to create a nicer error message: