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æREPL --- an interactive shell for Sophia

Try Sophia, test your contracts, check "what if", calculate a factorial. Completely offline, independently from remote networks, no dockers required.

If you are not familiar with Sophia, check its documentation first.




  • git
  • OTP 25 or 26
  • C++ compiler


Local build

Clone the repo:

git clone

Set up the environment:

export CXXFLAGS="-Wno-error=shadow -Wno-deprecated-copy -Wno-redundant-move -Wno-pessimizing-move"

Build the project (the make step may need to be executed twice, see this issue):

cd aerepl

Launch the REPL


Docker/podman image

For a consistent setup, a docker image can be created:

make docker

Then to start the dockerized REPL:

docker run -i aeternity/aerepl:local

Use make podman for a podman build.

CLI usage

æREPL usage patterns are highly inspired by GHCi. Most of the syntax is a direct adaptation of it to the needs of Sophia and FATE. This section shall provide an overview of the most fundamental features and typical workflows. If you find navigation clunky, please consider using rlwrap.

Main functionality of æREPL is to evaluate Sophia expressions:

AESO> 2 + 2

Aside from that, values can be assigned to REPL-local variables (pattern matching is supported)

AESO> let x = 2
AESO> let (q, w) = (x + 1, x - 1)

Functions and types are supported as well

AESO> record point = {x : int, y : int}
AESO> function get_x(p : point) = p.x
AESO> get_x({x = 100, y = 42})

NOTE: in-REPL functions cannot use in-REPL variables and other functions yet.


A common query is to ask about the type of an expression. This is done using the :type command:

AESO> :type Oracle.query
(oracle('a, 'b), 'a, int, Chain.ttl, Chain.ttl) => oracle_query('a, 'b)

Working with files

æREPL allows loading files to call their code and deploy contracts defined in them. To load a file, the :load command may be used:

// File: Test.aes
namespace N =
  function f() = 100

contract C =
  entrypoint f() = N.f() + 23
AESO> :load Test.aes
AESO> N.f()
AESO> let c = Chain.create() : C
AESO> c.f()

If multiple files are loaded, only the most recent one is brought to the scope. To include other loaded files into the working scope, Sophia's include should be used:

AESO> include "List.aes"

Note that :load reloads all listed files and unloads those skipped. Yet another useful command is :reload, which reloads all loaded files, preserving the included scope.

AESO> :load X.aes Y.aes
AESO> Y.y()  // defined in Y.aes
AESO> X.x()  // defined in X.aes
1:1 Unbound variable: X.x
AESO> include "X.aes"
AESO> X.x()  // Now it works

:load and :reload clear out the scope, meaning that they will clean

  • User defined variables
  • User defined functions
  • User defined types
  • Includes
  • Deployed contracts
  • In-REPL state

In-REPL state

æREPL maintains its own Sophia state which can be accessed using standard operations put and state, as well as stateful functions. By default, the state is set to () : unit. In order to change it to some other type, :state command should be used:

AESO> :set print_unit true
AESO> state
AESO> :state 1000
AESO> state + 1
AESO> put(state / 2)
AESO> state

Note that :state is parameterized by value, not by type. The value has to have a fully instantiated, non-functional type. Changing the state using the :state commands clears out all user-defined variables and functions --- if that is not desired, put should be used to modify the state if possible.


æREPL can be configured interactively using the :set command. The syntax for this command is :set OPTION [ARGS], for example

AESO> :set print_unit true

Currently the supported options are:

Option Arguments Description
call_gas non-neg int Determines the amount of gas to be supplied to each query.
------------------------- -------------------- :--------------------------------------------------------------------
call_value non-neg int The value, the amount of tokens supplied with the query.
------------------------- -------------------- :--------------------------------------------------------------------
call_gas_price non-neg int The result of Call.gas_price
------------------------- -------------------- :--------------------------------------------------------------------
call_origin pubkey The account to initiate execution of in-REPL code.
Defines Call.origin and initial Call.caller.
------------------------- -------------------- :--------------------------------------------------------------------
call_contract_creator pubkey The result of Contract.creator.
------------------------- -------------------- :--------------------------------------------------------------------
call_fee non-neg int The result of Call.fee.
------------------------- -------------------- :--------------------------------------------------------------------
call_height non-neg int The result of Chain.block_height.
------------------------- -------------------- :--------------------------------------------------------------------
print_gas true/false If true, REPL will print gas used for evaluating each expression.
------------------------- -------------------- :--------------------------------------------------------------------
print_format sophia/fate/json Determines the syntax used to display values.
------------------------- -------------------- :--------------------------------------------------------------------
print_unit true/false Whether to display unit (()).
------------------------- -------------------- :--------------------------------------------------------------------
print_type true/false Whether to display the type after each eval.
------------------------- -------------------- :--------------------------------------------------------------------
loc_backwards non-neg int Number of previous lines to be displayed when using location.
------------------------- -------------------- :--------------------------------------------------------------------
loc_forwards non-neg int Number of further lines to be displayed when using location.

Output format

By default, the REPL shall display values preserving compatibility with Sophia syntax. An exception from that rule are values containing functions which in FATE are represented as pairs of function name and closure. In that case, the output will take a form of "<fun $FUNHASH>" : $TYPE where $TYPE is the type of the function (according to the Sophia code, not FATE bytecode), and $FUNHASH is a hex-encoded shortcut of the original function's name hashed with BLAKE2B (as it is stored in the bytecode). For example

AESO> () => ()
"<fun E3472E14>" : () => unit

If print_format is set to fate, the value shall be displayed as an Erlang term that describes the exact representation of the value in the runtime.

AESO> :set print_format fate
AESO> record r = {x : int, y : int}
AESO> {y = 100, x = 7}
AESO> Some(1)
AESO> () => ()

If set to json, the values will be encoded in JSON format. Information about record fields and datatype constructor names shall not be dropped. Function values are represented as strings in the same manner as in the sophia format.

AESO> :set print_format json
AESO> record r = {x: int, y : int}
AESO> ({x = 3, y = 4}, "STRING")
    "x": 3,
    "y": 4

Multiline input

To type in a multiline block of code, surround it with :{ and :}:

AESO> :{
| let x = 123
| x
| :}

Generic server interface

If REPL is used as a library for a different tool, its generic server can be used for more structured interface. The server is located in src/aere_gen_server.erl and implements the standard gen_server Erlang behaviour.


Use aere_gen_server:start/1 to start up the server. aere_gen_server:start/2 allows to start a server under a custom name. The argument is property list with the following fields:

  • options --- parameter map for the repl configuration. See "Configuration" for more details.
  • accounts :: list(#{pubkey() => integer()}) --- list of initial accounts and their balances


  • quit --- terminates the server
  • skip --- does nothing
  • bump_nonce --- bumps internal REPL nonce (used in naming internal variables)
  • blockchain_state --- returns the chain state for the current session
  • theme --- returns the current display theme
  • {type, string()} --- parses the expression and returns its type in the session context
  • {state, string()} --- parses the expression and evaluates it in the session context. The restult is then assigned to the session's contract store. All locally defined functions, variables and types are pruned.
  • {eval, string()} --- parses the expression and evaluates it in the session context
  • {load, list(string())} --- Loads files from the file system. Includes the first one in the list.
  • reload --- Reloads the currently loaded files.
  • {set, Option :: atom(), Value :: list(term())} --- changes REPL's configuration (see {help, "set"} for more details)
  • help --- lists all available commands
  • {help, string()} --- returns the help text for the given command
  • {lookup, atom()} --- prints information about REPL's state or configuration
  • {disas, string()} --- parses a reference to a function and prints its FATE code
  • stop --- if at breakpoint, cancels the execution and rolls back all changes
  • {break, FileName :: string(), Line :: integer()} --- adds a breakpoint
  • {delete_break, integer()} --- removes a breakpoint with a given id
  • {delete_break_loc, string(), integer()} --- removes all breakpoints from the given file at the given line
  • continue --- resumes execution after a breakpoint stop
  • stepover --- proceeds to the next line in the current execution
  • stepin --- proceeds to the next line, or enters the function body if there is a function call upcoming
  • stepout --- resumes execution until the next breakpoint or current function return
  • location --- returns in-code location of current execution
  • {print_var, string()} --- returns in-code location of where the variable was introduced
  • print_vars --- returns values of all variables in scope
  • stacktrace --- returns the current stacktrace
  • {set_account, pubkey(), integer()} --- sets balance for an in-repl account
  • version --- returns version information
  • banner --- returns an ASCII "banner" presenting the REPL's logo and various version information


  • {update_filesystem_cache, #{string() => binary()}} --- updates REPL's perception of the file system to the provided map. If this is set, all include and file load instructions will ignore system's file system, and will use this map instead.


All above calls and casts are exposed as function calls for convenience. Additionally, the following are offered:

  • format --- formats outputs of other commands into renderable texts to be used by the render function
  • render --- renders a renderable output to a string using REPL's theme
  • banner --- returns a nicely rendered banner for CLI interfaces
  • input --- parses a text command and interprets it as one of the calls above. Useful for CLI-like interfaces.
  • prompt --- proposes prompt to display in the CLI based on the REPL's state. For example, the default is AESO> .