add bank-account exercise

bin/detect-unknown-words

@@ -88,16 +88,20 @@ def parse_solution(paths):
     text = '\n'.join(p.read_text() for p in paths if p.exists())
     defined, locals_ = set(), set()
 
-    # Top-level word definitions: `:` and `::`.
+    # Top-level word definitions: `:`, `::`, `TYPED:`, `TYPED::`.
     for m in re.finditer(r'^::?\s+(\S+)\s*\(', text, re.M):
         defined.add(m.group(1))
+    for m in re.finditer(r'^TYPED::?\s+(\S+)\s*\(', text, re.M):
+        defined.add(m.group(1))
     # Locals-bearing definitions:
     #   `:: <word> ( ... -- ... )`
     #   `M:: <class> <word> ( ... -- ... )`
+    #   `TYPED:: <word> ( name: class ... -- ... )`
     # The names aren't "defined" by `M::` (the generic was declared
-    # elsewhere), but the parameter list does introduce locals.
+    # elsewhere), but the parameter list does introduce locals. For
+    # `TYPED::` the class names also land in `locals_`, harmlessly.
     for m in re.finditer(
-        r'^(?:::\s+\S+|M::\s+\S+\s+\S+)\s*\(([^)]*)--[^)]*\)',
+        r'^(?:::\s+\S+|M::\s+\S+\s+\S+|TYPED::\s+\S+)\s*\(([^)]*)--[^)]*\)',
         text, re.M,
     ):
         for tok in m.group(1).split():

config.json

@@ -1625,6 +1625,18 @@
         ],
         "difficulty": 6
       },
+      {
+        "slug": "bank-account",
+        "name": "Bank Account",
+        "uuid": "d17aa096-63a8-4855-a8ee-f906a993a916",
+        "practices": [],
+        "prerequisites": [
+          "concurrency",
+          "errors",
+          "generics"
+        ],
+        "difficulty": 7
+      },
       {
         "slug": "book-store",
         "name": "Book Store",
@@ -1716,7 +1728,8 @@
           "higher-order-sequences",
           "curry-compose-fry",
           "errors",
-          "indexed-iteration"
+          "indexed-iteration",
+          "generics"
         ],
         "difficulty": 8
       },

exercises/practice/bank-account/.docs/instructions.md

@@ -0,0 +1,10 @@
+# Instructions
+
+Your task is to implement bank accounts supporting opening/closing, withdrawals, and deposits of money.
+
+As bank accounts can be accessed in many different ways (internet, mobile phones, automatic charges), your bank software must allow accounts to be safely accessed from multiple threads/processes (terminology depends on your programming language) in parallel.
+For example, there may be many deposits and withdrawals occurring in parallel; you need to ensure there are no [race conditions][wikipedia] between when you read the account balance and set the new balance.
+
+It should be possible to close an account; operations against a closed account must fail.
+
+[wikipedia]: https://en.wikipedia.org/wiki/Race_condition#In_software

exercises/practice/bank-account/.docs/introduction.md

@@ -0,0 +1,20 @@
+# Introduction
+
+After years of filling out forms and waiting, you've finally acquired your banking license.
+This means you are now officially eligible to open your own bank, hurray!
+
+Your first priority is to get the IT systems up and running.
+After a day of hard work, you can already open and close accounts, as well as handle withdrawals and deposits.
+
+Since you couldn't be bothered writing tests, you invite some friends to help test the system.
+However, after just five minutes, one of your friends claims they've lost money!
+While you're confident your code is bug-free, you start looking through the logs to investigate.
+
+Ah yes, just as you suspected, your friend is at fault!
+They shared their test credentials with another friend, and together they conspired to make deposits and withdrawals from the same account _in parallel_.
+Who would do such a thing?
+
+While you argue that it's physically _impossible_ for someone to access their account in parallel, your friend smugly notifies you that the banking rules _require_ you to support this.
+Thus, no parallel banking support, no go-live signal.
+Sighing, you create a mental note to work on this tomorrow.
+This will set your launch date back at _least_ one more day, but well...

exercises/practice/bank-account/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "bank-account/bank-account.factor"
+    ],
+    "test": [
+      "bank-account/bank-account-tests.factor"
+    ],
+    "example": [
+      ".meta/example.factor"
+    ]
+  },
+  "blurb": "Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!"
+}

exercises/practice/bank-account/.meta/example.factor

@@ -0,0 +1,49 @@
+USING: accessors concurrency.locks kernel math typed ;
+IN: bank-account
+
+TUPLE: bank-account open? balance lock ;
+
+: <bank-account> ( -- account )
+    bank-account new
+    f >>open?
+    0 >>balance
+    <lock> >>lock ;
+
+: check-open ( account -- )
+    open?>> [ "account not open" throw ] unless ;
+
+: check-positive ( amount -- )
+    0 <= [ "amount must be greater than 0" throw ] when ;
+
+TYPED:: open-account ( account: bank-account -- )
+    account lock>> [
+        account open?>> [ "account already open" throw ] when
+        account t >>open? 0 >>balance drop
+    ] with-lock ;
+
+TYPED:: close-account ( account: bank-account -- )
+    account lock>> [
+        account check-open
+        account f >>open? drop
+    ] with-lock ;
+
+TYPED:: balance ( account: bank-account -- n: integer )
+    account lock>> [
+        account check-open
+        account balance>>
+    ] with-lock ;
+
+TYPED:: deposit ( amount: integer account: bank-account -- )
+    account lock>> [
+        account check-open
+        amount check-positive
+        account [ amount + ] change-balance drop
+    ] with-lock ;
+
+TYPED:: withdraw ( amount: integer account: bank-account -- )
+    account lock>> [
+        account check-open
+        amount check-positive
+        amount account balance>> > [ "amount must be less than balance" throw ] when
+        account [ amount - ] change-balance drop
+    ] with-lock ;

exercises/practice/bank-account/.meta/generator.jl

@@ -0,0 +1,44 @@
+module BankAccount
+
+const EXTRA_VOCABS = ["concurrency.combinators", "locals", "sequences"]
+
+function fmt_op(op)
+    operation = op["operation"]
+    if operation == "open"
+        return "a open-account"
+    elseif operation == "close"
+        return "a close-account"
+    elseif operation == "deposit"
+        return "$(op["amount"]) a deposit"
+    elseif operation == "withdraw"
+        return "$(op["amount"]) a withdraw"
+    elseif operation == "balance"
+        return "a balance"
+    elseif operation == "concurrent"
+        inner = join(map(fmt_op, op["operations"]), " ")
+        return "$(op["number"]) <iota> [ drop $(inner) ] parallel-each"
+    else
+        error("unknown operation: " * operation)
+    end
+end
+
+function gen_test_case(case)
+    ops = case["input"]["operations"]
+    expected = case["expected"]
+    body = join(map(fmt_op, ops), "\n      ")
+    if expected isa AbstractDict        # { "error": "..." } — the last op throws
+        return """[
+    [let <bank-account> :> a
+      $(body)
+    ]
+] must-fail"""
+    else                                # the final `balance` op leaves the number
+        return """{ $(expected) } [
+    [let <bank-account> :> a
+      $(body)
+    ]
+] unit-test"""
+    end
+end
+
+end

exercises/practice/bank-account/.meta/tests.toml

@@ -0,0 +1,61 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[983a1528-4ceb-45e5-8257-8ce01aceb5ed]
+description = "Newly opened account has zero balance"
+
+[e88d4ec3-c6bf-4752-8e59-5046c44e3ba7]
+description = "Single deposit"
+
+[3d9147d4-63f4-4844-8d2b-1fee2e9a2a0d]
+description = "Multiple deposits"
+
+[08f1af07-27ae-4b38-aa19-770bde558064]
+description = "Withdraw once"
+
+[6f6d242f-8c31-4ac6-8995-a90d42cad59f]
+description = "Withdraw twice"
+
+[45161c94-a094-4c77-9cec-998b70429bda]
+description = "Can do multiple operations sequentially"
+
+[f9facfaa-d824-486e-8381-48832c4bbffd]
+description = "Cannot check balance of closed account"
+
+[7a65ba52-e35c-4fd2-8159-bda2bde6e59c]
+description = "Cannot deposit into closed account"
+
+[a0a1835d-faae-4ad4-a6f3-1fcc2121380b]
+description = "Cannot deposit into unopened account"
+
+[570dfaa5-0532-4c1f-a7d3-0f65c3265608]
+description = "Cannot withdraw from closed account"
+
+[c396d233-1c49-4272-98dc-7f502dbb9470]
+description = "Cannot close an account that was not opened"
+
+[c06f534f-bdc2-4a02-a388-1063400684de]
+description = "Cannot open an already opened account"
+
+[0722d404-6116-4f92-ba3b-da7f88f1669c]
+description = "Reopened account does not retain balance"
+
+[ec42245f-9361-4341-8231-a22e8d19c52f]
+description = "Cannot withdraw more than deposited"
+
+[4f381ef8-10ef-4507-8e1d-0631ecc8ee72]
+description = "Cannot withdraw negative"
+
+[d45df9ea-1db0-47f3-b18c-d365db49d938]
+description = "Cannot deposit negative"
+
+[ba0c1e0b-0f00-416f-8097-a7dfc97871ff]
+description = "Can handle concurrent transactions"