Normalizing CASE expression nodes. Refs #36

- `variant` `when` has a `condition` and a `consequent`
- `variant` `else` has just a `consequent`
- the outer `expression` is now `variant` `case` instead of `binary`
- instead of taking whatever is provided between `CASE` and `WHEN` (e.g., `CASE foo WHEN ...`) and calling that the expression, it is now added as `discriminant`

Author: nwronski

src/grammar.pegjs

@@ -594,34 +594,33 @@ expression_case "CASE Expression"
   {
     return Object.assign({
       'type': 'expression',
-      'format': 'binary',
       'variant': keyNode(t),
-      'condition': flattenAll([ w, s ])
+      'expression': flattenAll([ w, s ])
     }, e);
   }
 case_expression
   = !WHEN e:( expression ) {
     return {
-      'expression': e
+      'discriminant': e
     };
   }
 expression_case_when "WHEN Clause"
   = s:( WHEN ) o w:( expression ) o THEN o t:( expression ) o
   {
     return {
       'type': 'condition',
-      'format': keyNode(s),
-      'when': w,
-      'then': t
+      'variant': keyNode(s),
+      'condition': w,
+      'consequent': t
     };
   }
 expression_case_else "ELSE Clause"
   = s:( ELSE ) o e:( expression ) o
   {
     return {
       'type': 'condition',
-      'format': keyNode(s),
-      'else': e
+      'variant': keyNode(s),
+      'consequent': e
     };
   }