Added grammar for for loops

Since this needs to support assignment targets, it is difficult to
properly support this within a generic block syntax because of the
ability to create implicit tuples.

tatsu_grammar.txt

@@ -11,7 +11,7 @@ expressions
 
 expression
     =
-    content | raw_block_expression | block_expression | variable_expression | comment_expression
+    content | raw_block_expression | functional_block_expression | variable_expression | comment_expression
     ;
 
 raw_block_expression
@@ -31,6 +31,32 @@ raw_block_end
     block_open "endraw" block_close
     ;
 
+functional_block_expression
+    =
+    for_block_expression | block_expression
+    ;
+
+for_block_expression
+    =
+    for_block_start {SP}* expressions {SP}* for_block_end
+    ;
+
+for_block_start
+    =
+    block_open type:`blockstart` name:"for" {SP}* target:assignment_target {SP}* "in" {SP}* iter:variable_accessor_call_parameter_value [ {SP}* recursive:`True` "recursive" ] block_close
+    ;
+
+for_block_end
+    =
+    block_open "endfor" block_close
+    ;
+
+assignment_target
+    =
+    tuple+:block_parameter {"," {SP}* tuple+:block_parameter}+
+    | block_parameter
+    ;
+
 block_expression
     =
     block_start {SP}* expressions {SP}* block_end
@@ -39,7 +65,7 @@ block_expression
 
 block_start
     =
-    block_open type:`blockstart` !("end") name:IDENTIFIER parameters:[{block_parameter}*] block_close
+    block_open type:`blockstart` !("end") name:IDENTIFIER parameters:[ { block_parameter }* ] block_close
     ;
 
 block_end

test_template.jinja

@@ -14,7 +14,7 @@ across lines #}
 {% if False %}
 {{ '{{' }}
 {% endif %}
-{% for href caption in [('index.html', 'Index'), ('about.html', 'About'),
+{% for href, caption in [('index.html', 'Index'), ('about.html', 'About'),
                          ('downloads.html', 'Downloads')] %}
     <li><a href="{{ href }}">{{ caption }}</a></li>
 {% endfor %}