Add failing let expression corpus tests.

Resolving them may help with issue #1.

.gitignore

@@ -1,3 +1,5 @@
 node_modules
 build
 *.log
+corpus/broken-*.txt
+

corpus-broken/expression.txt

@@ -0,0 +1,26 @@
+========================================
+Let (nested with multiple `in`)
+========================================
+
+let x = e1 in let y = e2 in e3
+
+---
+
+(source_file (complete_expression (expression
+  (let (let_raw)) (label (simple_label)) (equal)
+    (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label))))))))))))))))))))))
+  (in (in_raw))
+  (let (let_raw)) (label (simple_label)) (equal)
+    (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label))))))))))))))))))))))
+  (in (in_raw))
+    (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label)))))))))))))))))))))))))
+
+========================================
+Let (label containing `in`)
+========================================
+
+let x = binary in e2
+
+---
+
+(source_file (complete_expression (expression (let (let_raw)) (label (simple_label)) (equal) (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label)))))))))))))))))))))) (in (in_raw)) (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label)))))))))))))))))))))))))

corpus/expression.txt

@@ -76,7 +76,7 @@ let x = e1 in e2
   (expression (annotated_expression (operator_expression (import_alt_expression (or_expression (plus_expression (text_append_expression (list_append_expression (and_expression (combine_expression (prefer_expression (combine_types_expression (times_expression (equal_expression (not_equal_expression (application_expression (import_expression (selector_expression (primitive_expression (identifier (label (simple_label)))))))))))))))))))))))))
 
 ========================================
-Let (nested)
+Let (nested with single `in`)
 ========================================
 
 let x = e1 let y = e2 in e3

grammar.js

@@ -90,6 +90,10 @@ module.exports = grammar({
     // ; according to the ordering of alternatives. That is, the order of evaluation,
     // ; of the alternatives is left-to-right.,
     // ;,
+
+    // TODO: Add a corpus test case for this and consider how to
+    // convey the left-to-right alternation preference to tree-sitter.
+
     // ; For example, the grammar for single quoted string literals is:,
     // ;,
     // ;     single-quote-continue =,
@@ -153,6 +157,11 @@ module.exports = grammar({
     // ; left-associative and all operators are left-associative when they are not,
     // ; parenthesized.,
     // ;,
+
+    // TODO: Consider how to test whether tree-sitter behaves this way
+    // and, if not, whether it can be persuaded to through a
+    // mechanical grammar translation.
+
     // ; Additionally, try alternatives in an order that minimizes backtracking,
     // ; according to the following rule:,
     // ;,