Only allow DeInit with empty head

.gitignore

@@ -1,4 +1,13 @@
+# Mac OS
+
 .DS_Store
+
+# Aiken 
+
 build
-.VSCodeCounter
 plutus.json
+
+# VSCode
+
+.VSCodeCounter
+.vscode

Makefile

@@ -0,0 +1,22 @@
+
+.PHONY: help
+help:
+	@echo "Usage: make <target>"
+	@echo
+	@echo "Targets:"
+	@echo "  help  -- show this help"
+	@echo "  shell -- start a nix development shell"
+	@echo "  build -- build the project"
+	@echo "  test -- test the project"
+
+.PHONY: shell
+shell:
+	nix shell github:aiken-lang/aiken#aiken
+
+.PHONY: build
+build:
+	aiken build
+
+.PHONY: test
+test:
+	aiken check

lib/linkedlist/linked_list.ak

@@ -4,7 +4,7 @@ use aiken/list
 use aiken/transaction.{Output}
 use aiken/transaction/value.{lovelace_of}
 use linkedlist/constants
-use linkedlist/types.{Common, Config, POSIXTime, PubKeyHash, SetNode}
+use linkedlist/types.{Common, Config, Empty, POSIXTime, PubKeyHash, SetNode}
 use linkedlist/utils
 
 pub fn init(common: Common) -> Bool {
@@ -21,7 +21,8 @@ pub fn init(common: Common) -> Bool {
 }
 
 pub fn deinit(common: Common) -> Bool {
-  let must_spend_exactly_one_node_input = list.length(common.node_inputs) == 1
+  expect [head_node] = common.node_inputs
+  expect Empty = head_node.node.next
   let must_not_produce_node_output = list.length(common.node_outputs) == 0
   let must_burn_correctly =
     utils.validate_mint(
@@ -30,7 +31,7 @@ pub fn deinit(common: Common) -> Bool {
       constants.origin_node_token_name,
       -1,
     )
-  must_spend_exactly_one_node_input? && must_not_produce_node_output? && must_burn_correctly?
+  must_not_produce_node_output? && must_burn_correctly?
 }
 
 pub fn insert(common: Common, insert_key: PubKeyHash, node: SetNode) -> Bool {

validators/sample.ak

@@ -158,6 +158,76 @@ test mint_validator_deinit() {
   mint_validator(config, redeemer, context)
 }
 
+test mint_validator_deinit_fails_on_non_empty() fail {
+  let own_cs = #"746fa3ba2daded6ab9ccc1e39d3835aa1dfcb9b5a54acc2ebe6b79a4"
+  let init_output_ref =
+    OutputReference {
+      transaction_id: TransactionId {
+        hash: #"2c6dbc95c1e96349c4131a9d19b029362542b31ffd2340ea85dd8f28e271ff6d",
+      },
+      output_index: 1,
+    }
+  let config =
+    Config {
+      init_utxo: init_output_ref,
+      deadline: 86_400_000,
+      penalty_address: Address(credential.ScriptCredential("P"), None),
+    }
+  let user2_pkh =
+    bytearray.from_string(
+      @"e18d73505be6420225ed2a42c8e975e4c6f9148ab38e951ea2572e54",
+    )
+  let user2_tn = "FSNe18d73505be6420225ed2a42c8e975e4c6f9148ab38e951ea2572e54"
+  let remove_output_ref =
+    OutputReference {
+      transaction_id: TransactionId { hash: #"" },
+      output_index: 1,
+    }
+  let remove_node =
+    SetNode { key: Key { key: user2_pkh }, next: Key { key: user2_pkh } }
+  let user2_value = value.add(value.zero(), own_cs, user2_tn, 1)
+  let remove_node_output =
+    Output {
+      address: Address(credential.ScriptCredential("I"), None),
+      value: value.add(
+        user2_value,
+        value.ada_policy_id,
+        value.ada_asset_name,
+        9_000_000,
+      ),
+      datum: InlineDatum(remove_node),
+      reference_script: None,
+    }
+  let burn_value = value.add(value.zero(), own_cs, origin_node_token_name, -1)
+  let redeemer = Deinit
+  let context =
+    ScriptContext {
+      purpose: Mint(own_cs),
+      transaction: Transaction {
+        inputs: [
+          Input {
+            output_reference: remove_output_ref,
+            output: remove_node_output,
+          },
+        ],
+        reference_inputs: [],
+        outputs: [],
+        fee: value.zero(),
+        mint: value.to_minted_value(burn_value),
+        certificates: [],
+        withdrawals: dict.new(),
+        validity_range: interval.everything(),
+        extra_signatories: [],
+        redeemers: dict.new(),
+        datums: dict.new(),
+        id: TransactionId {
+          hash: #"2c6dbc95c1e96349c4131a9d19b029362542b31ffd2340ea85dd8f28e271ff6d",
+        },
+      },
+    }
+  mint_validator(config, redeemer, context)
+}
+
 test mint_validator_insert() {
   let own_cs = #"746fa3ba2daded6ab9ccc1e39d3835aa1dfcb9b5a54acc2ebe6b79a4"
   let init_output_ref =