Welcome to turbine and the .streck language — your powerful toolkit for modeling, proving, and explaining the dynamics of complex financial scenarios. Whether you are working on interactions between companies, families, or other entities, Turbine helps you bring clarity, precision, and confidence to your financial reasoning.

Tutorial

The streck language is a language with statements, expressions and functions, concepts familiar for everyone who programmed in a computer language, for example Java or Go. The streck language however has one feature up its sleeve: The traditional programming concepts can coexist with a fourth construct: transactions. A transaction is a timestamped sequence of statements, a record of something not only referenced by a line number, but referenceable by its point in time as well. Transactions can be sorted by your computer and since it contains statements it can be executed by your computer as part of a simulation.

Let us have a look at what a hello world program written in streck looks like:

/*  helloworld.streck | illustrating streck and transactions. */

2025-07-14 11:00:00 print 'is this sorted correctly?\n'
2025-07-14 08:00:00 print 'Hello world 🤝 starting simulation.\n'
2025-07-14 17:00:00 print 'simulation end.\n'

prompt> turbine helloworld.streck
Hello world 🤝 starting simulation.
is this sorted correctly?
simulation end.
prompt>

/*  retrospect.streck | illustrating entity, time series and summation. */

2024-12-31 23:59:59 
  print 'Retrospect 🤝 starting simulation.\n'
  entity Company1 named 'My Company'
  account Company1.A1920 named 'Bank account'
  account Company1.A3010 named 'Domestic sales of goods'

2025-07-14 13:56:26 
  bookkeep Company1 {
    debit A1920 with 25000.00
    credit A3010 with 25000.00
  } comment 'A change in A1920 and A3010.'

2025-12-31 23:59:59 
  var result = SumYearCredit(Company1,A3010) - 
   SumYearDebit(Company1,A3010)
  print 'The yearly result is: \(result)\n'
  print 'simulation end.\n'

Retrospect 🤝 starting simulation.
The yearly result is: 25000.00
simulation end.

In .streck, we want to write readable code that is easy to understand so the language supports functions, a concept that is useful for two purposes: (1) To capture a parameterized sequence of statements that that can be reused from one or many transactions, and (2) to compute a value that is part of an expression. The first case is in computer science sometimes called a procedure and the second case is called a function. In .streck, we can add a procedure anywhere in a .streck file — even after its first use in a transaction. The normal way is to have the procedures at the beginning of a .streck file or in a separate file included from the command line. Since we have a very short program, we add the procedure to the beginning of the file as in

/*  coherence.streck | illustrating procedures. */

func Sale(priceInclVat) /* ⬷ a procedure. */
{
   bookkeep Company1 {
     debit A1920 with priceInclVat
     credit A3010 with priceInclVat
   } comment 'Interacting with customer.'
}

2024-12-31 23:59:59 
  print 'Coherence 🤝 starting simulation.\n'
  entity Company1 named 'My Company'
  account Company1.A1920 named 'Bank account'
  account Company1.A3010 named 'Domestic sales of goods'

2025-07-14 13:56:26 Sale(25000.00)
2025-07-14 15:56:26 Sale(25000.00)

2025-12-31 23:59:59 
  var result = SumYearCredit(Company1,A3010) - 
   SumYearDebit(Company1,A3010)
  print 'The yearly result is: \(result)\n'
  print 'simulation end.\n'

Coherence 🤝 starting simulation.
The yearly result is: 50000.00
simulation end.

As with procedures, a function can be defined anywhere in a .streck file or in a file included from the command line:

/*  compliance.streck | illustrating procedures and functions. */

func Gold(ounces, pricePerOunce) /* ⬷ a function. */
{
   return ounces * pricePerOunce
}

func SaleAndPayment_Gold(ounces, priceInclVat₋per₋ounce) /* ⬷ a procedure. */
{
  var priceExclVat = 0.8 * Gold(ounces,priceInclVat₋per₋ounce)
  var priceInclVat = 1.25 * priceExclVat
   
  bookkeep Company1 {
    debit A1510 with priceInclVat
    credit A2611 with priceInclVat - priceExclVat
    credit A3010 with priceExclVat
  } comment 'Sale Gold'
   
  bookkeep Company1 {
    credit A1510 with priceInclVat
    debit A1920 with priceInclVat
  } comment 'Payment Gold'
}

2024-12-31 23:59:59 
  print 'Compliance 🤝 starting simulation.\n'
  entity Company1 named 'My Company'
  account Company1.A1510 named 'Accounts Receivable'
  account Company1.A1920 named 'Bank account'
  account Company1.A2611 named 'Output VAT'
  account Company1.A3010 named 'Domestic sales of goods'

2025-07-14 13:56:26 SaleAndPayment_Gold(10, 3384.49)
2025-07-15 15:43:12 SaleAndPayment_Gold(10, 3373.38)
/* ⬷ the parameters are 'ounces' followed by 'price per ounce'. */

2025-12-31 23:59:59 
  var yearlyResult = SumYearCredit(Company1,A3010) -
   SumYearDebit(Company1,A3010)
  var assetsCash = SumYearDebit(Company1,A1920) - 
   SumYearCredit(Company1,A1920)
  print 'The result is: \(yearlyResult)\n'
  print 'The accumulation is: \(assetsCash)\n'
  print 'simulation end.\n'

Compliance 🤝 starting simulation.
The result is: 54062.96
The accumulation is: 67578.70
simulation end.

In the example above, we have four accounts, one function, and one procedure. Using the defined procedure SaleAndPayment_Gold, we can record both the sale of goods and the corresponding payment. We also output two values: yearlyResult and assetsCash, the latter representing accumulated funds expected to be carried forward to the daybook for future years.

We have now seen streck examples for documenting sales and purchases. We can also use turbine to compute the monthly Vat as in the following example:

/*  consistent.streck | VAT is closing the month. */

func SalesGoods25(priceExclVat)
{
  var priceInclVat = 1.25 * priceExclVat
   
  bookkeep Company1 {
    debit A1510 with priceInclVat
    credit A2611 with priceInclVat - priceExclVat
    credit A3010 with priceExclVat
  } comment 'Sale goods 25%.'
}

func ExpenseSnowClearance(priceInclVat) {
   
  var priceExclVat = 0.8 * priceInclVat
   
  bookkeep Company1 {
    debit A5164 with priceExclVat
    debit A2641 with priceInclVat - priceExclVat
    credit A2440 with priceInclVat
  } comment 'Expense snow clearance.'
}

func MonthlyVat() {
   
  var salesVat = SumMonthCredit(Company1,A2611)
  var purchaseVat = SumMonthDebit(Company1,A2641)
   
  bookkeep Company1 {
    debit A2611 with salesVat
    credit A2650 with salesVat
    credit A2641 with purchaseVat
    debit A2650 with purchaseVat
  } comment 'VAT January 2025'
   
  print 'The sales Vat is: \(salesVat)\n'
  print 'The purchase Vat is: \(purchaseVat)\n'
   
}

2024-12-31 23:59:59
   
  print 'Consistent 🤝 starting simulation.\n'
   
  entity Company1 named 'My Company'
   
  account Company1.A1510 named 'Accounts receivable'
  account Company1.A2440 named 'Accounts payable'
  account Company1.A2611 named 'Output VAT'
  account Company1.A2641 named 'Input VAT (Recoverable)'
  account Company1.A2650 named 'VAT payable/receivable'
  account Company1.A3010 named 'Domestic sales of goods'
  account Company1.A5164 named 'Snow-clearance'

2025-01-14 13:56:26 SalesGoods25(25000.00)
2025-01-14 13:56:26 ExpenseSnowClearance(18750.00)
2025-01-31 23:59:59 MonthlyVat()

2025-12-31 23:59:59
  print 'simulation end.\n'

Consistent 🤝 starting simulation.
The sales Vat is: 6250.00
The purchase Vat is: 3750.00
simulation end.

Additional Details on .streck

In this section, facets of the .streck language are described. We look at reserved words, the available predefined functions and other details.

Keywords

The streck language has fourteen plus five plus three keywords. A keyword has a special meaning in streck and can not be used as an identifier for a function, procedure, entity, or time series.

Five additional keywords are defined to construct transaction sequences:

And three keywords are reserved for handling change in accounting method:

A transaction sequence is by turbine ended before ending in case the ending is defined and before last transaction in case ending is not specified.

How to use the keywords are described in the Tutorial section in this document.

Predeclared Names

Eight functions are predeclared in streck: SumYearDebit, SumYearCredit, SumMonthDebit, SumMonthCredit, SumDayDebit, SumDayCredit, SumAllDebit, SumAllCredit. Each function accepts an entity identifier as its first argument and a time series key as its second argument.

Identifiers

An identifier in streck is a Unicode token that does not begin with a digit.

Command-Line Usage

You can specify multiple .streck files as arguments when running turbine from the command line as in

prompt> turbine definition.streck daybook-2025-and-closing.streck

Revision Handling and .streck

Your streck files are UTF-8 encoded text files. This means your work can be tracked with for example the Git revision handling system.