Add associative map constraints and range refinement

doc/manual/souce/language/grammar.md

@@ -35,8 +35,9 @@ module          = { statement } ;
 statement       = field_definition , [ ";" ]
                 | expression , [ ";" ] ;
 
-expression      = default_expression ;
+expression      = as_expression ;
 
+as_expression      = default_expression , { "as" , default_expression } ;
 default_expression = patch_expression , [ "default" , default_expression ] ;
 patch_expression   = compose_expression , { "//" , compose_expression } ;
 compose_expression = logical_or_expression , { "&" , logical_or_expression } ;
@@ -56,6 +57,7 @@ path_suffix        = "." , identifier ;
 primary_expression = literal
                    | identifier
                    | comparison_constraint
+                   | map_constraint
                    | object
                    | array_constraint
                    | array
@@ -70,6 +72,7 @@ comparison_operator = "==" | "!=" | "<" | "<=" | ">" | ">=" ;
 comparison_constraint = ( "<" | "<=" | ">" | ">=" ) , expression ;
 
 object             = "{" , [ field_definition , { ";" , field_definition } , [ ";" ] ] , "}" ;
+map_constraint     = "{" , "..." , expression , "}" ;
 field_definition   = field_path , "=" , expression ;
 field_path         = identifier , { "." , identifier } ;
 
@@ -104,6 +107,7 @@ Precedence is highest first.
 9. `&`
 10. `//`
 11. `default`
+12. `as`
 
 Binary operators are left-associative except `default`, which is right-associative.