Add type declarations

For now, simplified to type aliases only.

src/grammar.json

@@ -1045,6 +1045,13 @@
       "content": {
         "type": "CHOICE",
         "members": [
+          {
+            "type": "REPEAT1",
+            "content": {
+              "type": "SYMBOL",
+              "name": "type_declaration"
+            }
+          },
           {
             "type": "REPEAT1",
             "content": {
@@ -1072,6 +1079,48 @@
         ]
       }
     },
+    "type_declaration": {
+      "type": "SEQ",
+      "members": [
+        {
+          "type": "STRING",
+          "value": "type"
+        },
+        {
+          "type": "FIELD",
+          "name": "name",
+          "content": {
+            "type": "SYMBOL",
+            "name": "identifier"
+          }
+        },
+        {
+          "type": "STRING",
+          "value": "="
+        },
+        {
+          "type": "FIELD",
+          "name": "value",
+          "content": {
+            "type": "SYMBOL",
+            "name": "_type"
+          }
+        }
+      ]
+    },
+    "_type": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "SYMBOL",
+          "name": "type_alias"
+        }
+      ]
+    },
+    "type_alias": {
+      "type": "SYMBOL",
+      "name": "identifier"
+    },
     "function_declaration": {
       "type": "SEQ",
       "members": [

src/node-types.json

@@ -1357,6 +1357,10 @@
             "type": "primitive_declaration",
             "named": true
           },
+          {
+            "type": "type_declaration",
+            "named": true
+          },
           {
             "type": "variable_declaration",
             "named": true
@@ -1740,6 +1744,10 @@
           "type": "string_literal",
           "named": true
         },
+        {
+          "type": "type_declaration",
+          "named": true
+        },
         {
           "type": "unary_expression",
           "named": true
@@ -1770,6 +1778,47 @@
       ]
     }
   },
+  {
+    "type": "type_alias",
+    "named": true,
+    "fields": {},
+    "children": {
+      "multiple": false,
+      "required": true,
+      "types": [
+        {
+          "type": "identifier",
+          "named": true
+        }
+      ]
+    }
+  },
+  {
+    "type": "type_declaration",
+    "named": true,
+    "fields": {
+      "name": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "identifier",
+            "named": true
+          }
+        ]
+      },
+      "value": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "type_alias",
+            "named": true
+          }
+        ]
+      }
+    }
+  },
   {
     "type": "unary_expression",
     "named": true,
@@ -2250,6 +2299,10 @@
     "type": "to",
     "named": false
   },
+  {
+    "type": "type",
+    "named": false
+  },
   {
     "type": "var",
     "named": false