Ergo Language Reference
Lexical conventions
File Extension
Ergo files have the .ergo
extension.
Blanks
Blank characters (such as space, tabulation, carriage return) are ignored but they are used to separate identifiers.
Comments
Comments come in two forms. Single line comments are introduced by the
two characters //
and are terminated by the end of the current
line. Multi-line comments start with the two characters /*
and are
terminated by the two characters */
. Multi-line comments can be
nested.
Here are examples of comments:
// This is a single line comment
/* This comment spans multiple lines
and it can also be /* nested */ */
Reserved words
The following are reserved as keywords in Ergo. They cannot be used as identifiers.
namespace, import, define, function, transaction, concept, event, asset,
participant, enum, extends, contract, over, clause, throws, emits, state, call,
enforce, if, then, else, let, foreach, return, in, where, throw,
constant, match, set, emit, with, or, and, true, false, unit, none
Condition Expressions
Conditional statements, conditional expressions and conditional constructs are features of a programming language which perform different computations or actions depending on whether a programmer-specified boolean condition evaluates to true or false. Conditional expressions (also known as if
statements) allow us to conditionally execute Ergo code depending on the value of a test condition. If the test condition evaluates to true
then the code on the then
branch is evaluated. Otherwise, when the test condition evaluates to false
then the else
branch is evaluated.
Example
if delayInDays > 15.0 then
BuyerMayTerminateResponse{};
else
BuyerMayNotTerminateResponse{}
Legal Prose
For example, this corresponds to a conditional logic statement in legal prose.
If the delay is more than 15 days, the Buyer is entitled to terminate this Contract.
Syntax
if expression1 then // Condition
expression2 // Expression if condition is true
else
expression3 // Expression if condition is false
Where expression1
is an Ergo expression that evaluates to a Boolean
value (i.e. true
or false
), and expression2
and expression3
are
Ergo expressions.
Note that as with all Ergo expressions, new lines and indentation don't change the meaning of your code. However it is good practice to standardise the way that you using whitespace in your code to make it easier to read.
Usage
If statements can be chained , i.e., if ... then .... else if ... then ... else ...
to build more compound conditionals.
if request.netAnnualChargeVolume < contract.firstVolume then
return VolumeDiscountResponse{ discountRate: contract.firstRate }
else if request.netAnnualChargeVolume < contract.secondVolume then
return VolumeDiscountResponse{ discountRate: contract.secondRate }
else
return VolumeDiscountResponse{ discountRate: contract.thirdRate }
Conditional expressions can also be used as expressions, e.g., inside a constant declaration:
define constant price = 42;
define constant message = if price >i 100 then "High price" else "Low Price";
message;
The value of message after running this code will be "Low Price"
.
Related
- Match expression - where many alternative conditions check the same variable
Match Expressions
Match expressions allow us to check an expression against multiple possible values or patterns. If a match is found, then Ergo will evaluate the corresponding expression.
Match expressions are similar to
switch
statements in other programming languages
Example
match request.status
with "CREATED" then
new PayOut{ amount : contract.deliveryPrice }
with "ARRIVED" then
new PayOut{ amount : contract.deliveryPrice - shockPenalty }
else
new PayOut{ amount : 0.0 }
Legal Prose
Example needed.
Syntax
match expression0
with pattern1 then // Repeat this line
expression1 // and this line
else
expression2
Usage
You can use a match expression to look for patterns based on the type of an expression.
match response
with let b1 : BuyerMayTerminateResponse then
// Do something with b1
with let b2 : BuyerMayNotTerminateResponse then
// Do something with b2
else
// Do a default action
You can use it to match against an optional value.
match maybe_response
with let? b1 : BuyerMayTerminateResponse then
// Do something when there is a response
else
// Do something else when there is no response
Often a match expression is a more concise way to represent a conditional expression with a repeating, regular condition. For example:
if x = 1 then
...
else if x = 2 then
...
else if x = 3 then
...
else if x = 4 then
...
else
...
This is equivalent to the match expression:
match x
with 1 then
...
with 2 then
...
with 3 then
...
with 4 then
...
else
...