Script Constructor

Questions
1

module Refer where

import Daml.Script
import DA.Time
import DA.Date

native_test : Script ()
native_test = script do
alice ← allocateParty “Alice”
bob ← allocateParty “Bob”
let
my_int = -123
my_dec = 0.001 : Decimal
my_text = “Alice”
my_bool = False
my_date = date 2020 Jan 01
my_time = time my_date 00 00 00
my_rel_time = hours 24

assert (-my_int == 123)
assert (1000.0 * my_dec == 1.0)
assert (my_text == “Alice”)
assert (not my_bool)
assert (addDays my_date 1 == date 2020 Jan 02)
assert (addRelTime my_time my_rel_time == time (addDays my_date 1) 00 00 00)

Is below the way to trigger above script, if not plz correct my understanding.

daml script --dar .daml/dist/create-daml-app-0.1.0.dar --script-name Refer:native_test --ledger-host localhost --ledger-port 6865

Also,
what is the purpose of having constructor first and then script with do keyword.

2

Yes, that is the correct invocation.

What do you call “constructor” in this case?

3

@kanika_kapoor, perhaps some explanation of these two lines would be helpful?

native_test : Script ()
native_test = script do
    :
  • The line native_test : Script () declares the type of the “variable” named native_test.
  • The line native_test = script do begins the binding of a value to that variable.

A similar example could be the following:

x : Int
x = 3

You could alternatively do this:

x : Int = 3

native_test : Script () = script do
    :

And in many cases you can leave out the type declaration and the compiler will infer the type.

x = 3

native_test = script do
    :
4

I would strongly advise you to never leave out the type for top-level declarations.