Second commit.

grammar.js

@@ -1,5 +1,5 @@
 /**
- * @file Scl grammar for tree-sitter
+ * @file SCL grammar for tree-sitter
  * @author Jacob Signorovitch <jacob.signorovitch@gmail.com>
  * @license MIT
  */
@@ -7,11 +7,108 @@
 /// <reference types="tree-sitter-cli/dsl" />
 // @ts-check
 
+// grammar.js
+const PREC = {
+  assign: 0, // right-assoc
+  add: 1, // left-assoc
+  mul: 2, // left-assoc
+  call: 3,
+  funcdef: 4,
+  lambda: 5,
+};
+
 module.exports = grammar({
   name: "scl",
 
+  // Whitespace is of no consequence.
+  extras: ($) => [/\s/],
+
+  conflicts: ($) => [[$.params, $._exp]],
+
   rules: {
-    // TODO: add the actual grammar rules
-    source_file: $ => "hello"
-  }
+    // A file is zero or more expressions.
+    source_file: ($) => repeat($._exp),
+
+    // Everything is expressions. Makes this a lot easier.
+    _exp: ($) =>
+      choice(
+        $.num,
+        $.word,
+        $.binexp,
+        $.callexp,
+        $.funcdef,
+        $.lambda,
+        $.vardef,
+        $.parexp,
+      ),
+
+    // Literals / identifiers.
+    num: (_) => /\d+/,
+    word: (_) => /[a-zA-Z_]\w*/,
+
+    // Binary expressions with precedence and left associativity.
+    binexp: ($) =>
+      choice(
+        prec.left(
+          PREC.add,
+          seq(
+            field("left", $._exp),
+            field("op", choice("+", "-")),
+            field("right", $._exp),
+          ),
+        ),
+        prec.left(
+          PREC.mul,
+          seq(
+            field("left", $._exp),
+            field("op", choice("*", "/")),
+            field("right", $._exp),
+          ),
+        ),
+      ),
+
+    // Function call: prefer this over plain `word` via precedence.
+    callexp: ($) =>
+      prec(
+        PREC.call,
+        seq(field("fn", $.word), "(", optional(commaSep($._exp)), ")"),
+      ),
+
+    // Convenient function definition (sugar): `f(x, y, ...) body`.
+    // Give it higher precedence than calls to resolve the shared prefix.
+    funcdef: ($) =>
+      prec(
+        PREC.funcdef,
+        seq(
+          field("name", $.word),
+          field("params", $.params),
+          field("body", $._exp),
+        ),
+      ),
+
+    // Lambda: `\(x, y, ...) body`.
+    lambda: ($) =>
+      prec(
+        PREC.lambda,
+        seq("\\", field("params", $.params), field("body", $._exp)),
+      ),
+
+    // Variable definition / assignment: `x = expr`.
+    // Lowest precedence, right-associative: `a = b = c` → `a = (b = c)`.
+    vardef: ($) =>
+      prec.right(
+        PREC.assign,
+        seq(field("name", $.word), "=", field("value", $._exp)),
+      ),
+
+    // Parameter list node used by funcdef and lambda.
+    params: ($) => seq("(", optional(commaSep($.word)), ")"),
+
+    // Parenthesized expression.
+    parexp: ($) => seq("(", $._exp, ")"),
+  },
 });
+
+function commaSep(rule) {
+  return seq(rule, repeat(seq(",", rule)));
+}