DAML REPL¶

WARNING: DAML REPL is an early access feature that is actively being designed and is subject to breaking changes. We welcome feedback about the DAML REPL on our issue tracker or on our forum or on Slack.

The DAML REPL allows you to use the DAML Script API interactively. This is useful for debugging and for interactively inspecting and manipulating a ledger.

Usage¶

First create a new project based on the script-example template. Take a look at the documentation for DAML Script for details on this template.

daml new script-example script-example # create a project called script-example based on the template
cd script-example # switch to the new project

Now, build the project and start DAML Sandbox, the in-memory ledger included in the DAML SDK. Note that we are starting Sandbox in wallclock mode. Static time is not supported in daml repl.

daml build
daml sandbox --wall-clock-time --port=6865 .daml/dist/script-example-0.0.1.dar

Now that the ledger has been started, you can launch the REPL in a separate terminal using the following command.

daml repl --ledger-host=localhost --ledger-port=6865 .daml/dist/script-example-0.0.1.dar

The --ledger-host and --ledger-port parameters point to the host and port your ledger is running on. In addition to that, you also need to pass in the name of a DAR containing the templates and other definitions that will be accessible in the REPL.

You should now see a prompt looking like

daml>

You can think of this prompt like a line in a do-block of the Script action. Each line of input has to have one of the following two forms:

An expression expr of type Script a for some type a. This will execute the script ignoring the result.
A binding of the form pat <- expr where pat is pattern, e.g., a variable name x to bind the result to and expr is an expression of type Script a. This will execute the script and match the result against the pattern pat bindings the matches to the variables in the pattern. You can then use those variables on subsequent lines.

First create two parties: A party with the display name "Alice" and the party id "alice" and a party with the display name "Bob" and the party id "bob".

daml> alice <- allocatePartyWithHint "Alice" (PartyIdHint "alice")
daml> bob <- allocatePartyWithHint "Bob" (PartyIdHint "bob")

Next, create a CoinProposal from Alice to Bob

daml> submit alice (createCmd (CoinProposal (Coin alice bob)))

As Bob, you can now get the list of active CoinProposal contracts using the query function. The debug : Show a => a -> Script () function can be used to print values.

daml> proposals <- query @CoinProposal bob
daml> debug proposals
[Daml.Script:39]: [(<contract-id>,CoinProposal {coin = Coin {issuer = 'alice', owner = 'bob'}})]

Finally, accept all proposals using the forA function to iterate over them.

daml> forA proposals $ \(contractId, _) -> submit bob (exerciseCmd contractId Accept)

Using the query function we can now verify that there is one Coin and no CoinProposal:

daml> coins <- query @Coin bob
daml> debug coins
[Daml.Script:39]: [(<contract-id>,Coin {issuer = 'alice', owner = 'bob'})]
daml> proposals <- query @CoinProposal bob
[Daml.Script:39]: []

To exit daml repl press Control-D.

What is in scope at the prompt?¶

In the prompt, all modules from the main dalf of the DAR passed to daml repl are imported. In addition to that the Daml.Script module is imported and gives you access to the DAML Script API.

You can use import declarations at the prompt to import additional modules.

daml> import DA.Time
daml> debug (days 1)

Connecting via TLS¶

You can connect to a ledger that requires TLS by passing --tls. A custom root certificate used for validating the server certificate can be set via --cacrt. Finally, you can also enable client authentication by passing --pem client.key --crt client.crt. If --cacrt or --pem and --crt are passed TLS is automatically enabled so --tls is redundant.

Connection to a Ledger with Authentication¶

If your ledger requires an authentication token you can pass it via --access-token-file.