Reference: built-in functions

This page gives reference information on functions for.

Working with time

DAML has these built-in functions for working with time:

  • datetime: creates a Time given year, month, day, hours, minutes, and seconds as argument.
  • subTime: subtracts one time from another. Returns the RelTime difference between time1 and time2.
  • addRelTime: add times. Takes a Time and RelTime and adds the RelTime to the Time.
  • days, hours, minutes, seconds: constructs a RelTime of the specified length.
  • pass: (in scenario tests only) use pass : RelTime -> Scenario Time to advance the ledger time by the argument amount. Returns the new time.

Working with numbers

DAML has these built-in functions for working with numbers:

  • round: rounds a Decimal number to Int.

    round d is the nearest Int to d. Tie-breaks are resolved by rounding away from zero, for example:

    round 2.5 == 3    round (-2.5) == -3
round 3.4 == 3    round (-3.7) == -4

  • truncate: converts a Decimal number to Int, truncating the value towards zero, for example:

    truncate 2.2 == 2    truncate (-2.2) == -2
truncate 4.9 == 4    v (-4.9) == -4

  • intToDecimal: converts an Int to Decimal.

The set of numbers expressed by Decimal is not closed under division as the result may require more than 10 decimal places to represent. For example, 1.0 / 3.0 == 0.3333... is a rational number, but not a Decimal.

Working with text

DAML has these built-in functions for working with text:

  • <> operator: concatenates two Text values.
  • show converts a value of the primitive types (Bool, Int, Decimal, Party, Time, RelTime) to a Text.

To escape text in DAML strings, use \:

Character How to escape it
\ \\
" \"
' \'
Newline \n
Tab \t
Carriage return \r
Unicode (using ! as an example)
  • Decimal code: \33
  • Octal code: \o41
  • Hexadecimal code: \x21

Working with lists

DAML has these built-in functions for working with lists:

  • foldl and foldr: see Folding below.

Folding

A fold takes:

  • a binary operator
  • a first accumulator value
  • a list of values

The elements of the list are processed one-by-one (from the left in a foldl, or from the right in a foldr).

Note

We’d usually recommend using foldl, as foldr is usually slower. This is because it needs to traverse the whole list before starting to discharge its elements.

Processing goes like this:

  1. The binary operator is applied to the first accumulator value and the first element in the list. This produces a second accumulator value.
  2. The binary operator is applied to the second accumulator value and the second element in the list. This produces a third accumulator value.
  3. This continues until there are no more elements in the list. Then, the last accumulator value is returned.

As an example, to sum up a list of integers in DAML:

sumList =
  scenario do
    assert (foldl (+) 0 [1, 2, 3] == 6)