The simplest kind of expressions in Ergo are literal values.
"John Smith" // a String literal 1 // an Integer literal 3.0 // a Double literal 3.5e-10 // another Double literal true // the Boolean true false // the Boolean false
Each line here is a separate expression. At the end of the line, the notation
// write something here is a comment, which means it is a part of your Ergo program which is ignored by the Ergo compiler. It can be useful to document your code.
Every Ergo expression can be evaluated, which means it should compute some value. In the case of a literal value, the result of evaluation is simply itself (e.g., the expression
1 evaluates to the integer
You can actually see the result of evaluating expressions by trying them out in the Ergo REPL. You just have to prefix them with
return: for instance, to evaluate the String literal
return "John Smith"(followed by clicking the button 'Evaluate') in the REPL. This should answer:
Response. "John Smith" : String.
You can apply operators to values. Those can be used for arithmetic operations, to compare two values, to concatenate two string values, etc.
1.0 + 2.0 * 3.0 // arithmetic operators on Double -1.0 1 + 2 * 3 // arithmetic operators on Integer -1 1.0 <= 3.0 // comparison operators on Double 1.0 = 2.0 2.0 > 1.0 1 <= 3 // comparison operators on Integer 1 = 2 2 > 1.0 true or false // Boolean disjunction true and false // Boolean conjunction !true // Negation "Hello" ++ " World!" // String concatenation
Again, you can try those in the Ergo REPL. For instance, typing
return true and falseshould answer
Response. false : Boolean, and typing
return 1.0 + 2.0 * 3.0should answer:
Response. 7.0 : Double.
Conditional expressions can be used to perform different computations depending on some condition:
if 1.0 < 0.0 // Condition then "negative" // Expression if condition is true else "positive" // Expression if condition is false
return if 1.0 < 0.0 then "negative" else "positive"in the Ergo REPL, should answer
Response. "positive" : String.
See also the Conditional Expression Reference
Local variables can be declared with
let x = 1; // declares and initialize a variable x+2 // rest of the expression, where x is in scope
Let bindings give a name to some intermediate result and allows you to reuse the corresponding value in multiple places:
let x = -1.0; // bind x to the value -1.0 if x < 0.0 // if x is negative then -x // then return the opposite of x else x // else return x
TechNote: let bindings in Ergo are immutable, in a way similar to other functional languages. A nice explanation can be found e.g., in the documentation for let bindings in ReasonML.