Add let expressions

corpus/expressions.txt

@@ -138,6 +138,23 @@ or = x \/ y;
   (assignment (identifier) (infix_operator (identifier) (identifier)))
   (assignment (identifier) (infix_operator (identifier) (identifier))))
 
+==============
+Let Expression
+==============
+
+empty = let {} in 1;
+var_offset = let {var int: a;} in a + 3;
+constrained = let {constraint x = y} in x;
+multiple = let {var int: a, var int: b} in a + b;
+
+---
+
+(source_file
+  (assignment (identifier) (let_expression (integer_literal)))
+  (assignment (identifier) (let_expression (declaration (base_type (primitive_type)) (identifier)) (infix_operator (identifier) (integer_literal))))
+  (assignment (identifier) (let_expression (constraint (infix_operator (identifier) (identifier))) (identifier)))
+  (assignment (identifier) (let_expression (declaration (base_type (primitive_type)) (identifier)) (declaration (base_type (primitive_type)) (identifier)) (infix_operator (identifier) (identifier)))))
+
 ===========
 Precedences
 ===========

grammar.js

@@ -89,6 +89,7 @@ module.exports = grammar({
         $.if_then_else,
         $.indexed_access,
         $.infix_operator,
+        $.let_expression,
         $.prefix_operator,
         $.set_comprehension,
         $.string_interpolation,
@@ -193,6 +194,19 @@ module.exports = grammar({
       );
     },
 
+    let_expression: ($) =>
+      seq(
+        "let",
+        "{",
+        field(
+          "let",
+          sepBy(choice(",", ";"), choice($.declaration, $.constraint))
+        ),
+        "}",
+        "in",
+        field("in", $._expression)
+      ),
+
     prefix_operator: ($) =>
       prec(
         PREC.unary,

src/grammar.json

@@ -266,6 +266,10 @@
           "type": "SYMBOL",
           "name": "infix_operator"
         },
+        {
+          "type": "SYMBOL",
+          "name": "let_expression"
+        },
         {
           "type": "SYMBOL",
           "name": "prefix_operator"
@@ -1245,6 +1249,99 @@
         }
       ]
     },
+    "let_expression": {
+      "type": "SEQ",
+      "members": [
+        {
+          "type": "STRING",
+          "value": "let"
+        },
+        {
+          "type": "STRING",
+          "value": "{"
+        },
+        {
+          "type": "FIELD",
+          "name": "let",
+          "content": {
+            "type": "SEQ",
+            "members": [
+              {
+                "type": "REPEAT",
+                "content": {
+                  "type": "SEQ",
+                  "members": [
+                    {
+                      "type": "CHOICE",
+                      "members": [
+                        {
+                          "type": "SYMBOL",
+                          "name": "declaration"
+                        },
+                        {
+                          "type": "SYMBOL",
+                          "name": "constraint"
+                        }
+                      ]
+                    },
+                    {
+                      "type": "CHOICE",
+                      "members": [
+                        {
+                          "type": "STRING",
+                          "value": ","
+                        },
+                        {
+                          "type": "STRING",
+                          "value": ";"
+                        }
+                      ]
+                    }
+                  ]
+                }
+              },
+              {
+                "type": "CHOICE",
+                "members": [
+                  {
+                    "type": "CHOICE",
+                    "members": [
+                      {
+                        "type": "SYMBOL",
+                        "name": "declaration"
+                      },
+                      {
+                        "type": "SYMBOL",
+                        "name": "constraint"
+                      }
+                    ]
+                  },
+                  {
+                    "type": "BLANK"
+                  }
+                ]
+              }
+            ]
+          }
+        },
+        {
+          "type": "STRING",
+          "value": "}"
+        },
+        {
+          "type": "STRING",
+          "value": "in"
+        },
+        {
+          "type": "FIELD",
+          "name": "in",
+          "content": {
+            "type": "SYMBOL",
+            "name": "_expression"
+          }
+        }
+      ]
+    },
     "prefix_operator": {
       "type": "PREC",
       "value": 13,

src/node-types.json

@@ -51,6 +51,10 @@
         "type": "integer_literal",
         "named": true
       },
+      {
+        "type": "let_expression",
+        "named": true
+      },
       {
         "type": "parenthesised_expression",
         "named": true
@@ -640,6 +644,44 @@
       }
     }
   },
+  {
+    "type": "let_expression",
+    "named": true,
+    "fields": {
+      "in": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "_expression",
+            "named": true
+          }
+        ]
+      },
+      "let": {
+        "multiple": true,
+        "required": false,
+        "types": [
+          {
+            "type": ",",
+            "named": false
+          },
+          {
+            "type": ";",
+            "named": false
+          },
+          {
+            "type": "constraint",
+            "named": true
+          },
+          {
+            "type": "declaration",
+            "named": true
+          }
+        ]
+      }
+    }
+  },
   {
     "type": "output",
     "named": true,
@@ -1012,6 +1054,10 @@
     "type": "intersect",
     "named": false
   },
+  {
+    "type": "let",
+    "named": false
+  },
   {
     "type": "maximize",
     "named": false