[#52] Allow pattern matching in case expressions (#53)

Author: jonhue

grammar.js

@@ -273,7 +273,10 @@ module.exports = grammar({
       '->',
       choice(
         seq('[', field('right', $._simple_expression), ']'),
-        field('right', alias($.identifier, $.shorthand_access_identifier))
+        field('right', choice(
+          alias($.identifier, $.shorthand_access_identifier),
+          $.number)
+        )
       )
     )),
 
@@ -336,11 +339,11 @@ module.exports = grammar({
     ),
     when_clause: $ => seq(
       'when',
-      field('values', $.expression_list),
+      field('values', $.pattern_list),
       optional('then'),
       field('consequence', $.block)
     ),
-    expression_list: $ => commaSep1($._simple_expression),
+    pattern_list: $ => commaSep1($.pattern),
 
     module: $ => seq('module', field('body', $.block)),
 

test/corpus/expressions.txt

@@ -367,12 +367,16 @@ a.b.c(1)
 access
 ==================
 
+a->0
 a->b(1)
 a.b->[c]
 
 ---
 
 (program
+  (access
+      left: (identifier)
+      right: (number))
   (application
     abstraction: (access
       left: (identifier)
@@ -497,8 +501,8 @@ a := case a
        1
 
 case a
-when 1
-  1
+when [1, a]
+  a
 when 1, 1 then 1
 else 1
 
@@ -511,22 +515,30 @@ else 1
       value: (identifier)
       branches: (when_clauses
         (when_clause
-          values: (expression_list
-            (number))
+          values: (pattern_list
+            (pattern
+              value: (number)))
           consequence: (block
             (number))))))
   (case
     value: (identifier)
     branches: (when_clauses
       (when_clause
-        values: (expression_list
-          (number))
+        values: (pattern_list
+          (pattern
+            pattern: (list_pattern
+              (pattern
+                value: (number))
+              (pattern
+                name: (identifier_pattern)))))
         consequence: (block
-          (number)))
+          (identifier)))
       (when_clause
-        values: (expression_list
-          (number)
-          (number))
+        values: (pattern_list
+          (pattern
+            value: (number))
+          (pattern
+            value: (number)))
         consequence: (block
           (number))))
     default: (block