The Program class is the entry point of the interpreter. The process of executing code goes through the following steps:
- Lexer: scans the input into tokes
- Parser: uses an operator-precedence parser to construct the AST
- Transformers:
- ClosureTransformer: adds closures to function definitions
- ShadowReferenceTransformer: renames variables to prevent shadowing
- LiteralOptimizerTransformer: rewrites expressions who's leaves are all literals to one single literal
- Runtime: executes the code with a treewalker
There are four runtime types in this language: Number, Bool, Null and Function. Values are loosely typed and will be converted when needed:
| value | Number | Bool | Function |
|---|---|---|---|
| 0 | self |
false |
_ -> self |
| 1 | self |
true |
_ -> self |
| Number | self |
error | _ -> self |
| true | 1 |
self |
_ -> self |
| false | 0 |
self |
_ -> self |
| null | error | error | error |
| Function | error | error | self |
Bools are constructed by the true and false keyword. A null value can be created with null. Numbers are created via literal values, e.g. 1 or 42
Variables are dynamicly typed, have lexial scoping and can shadow other variables. A variable is delecared with let name := expression;, where the expression will be strictly evaluated. Variables can be updated with name := expression;. Both variable declaration and assignment are statements, but a statement can be converted into an expression by wrapping it in a block expression: let a := { b := 42; };. The value of a here will be null
Algebraic:
3 / 2
1 + 2 * 3
3 - 9
Comparison:
1 = 1
1 != 2
1 < 2
2 > 1
Boolean:
1 = 1 | 2 = 4
1 = 1 & 2 = 4
!1
Parentheses:
(1 + 2) * 3
Functions
A function is declared with a single parameter name and an arrow. They have their own lexial scoping when the ClosureTransformer is being used.
a -> a + 2
a -> b -> a + b
A function is called by providing its formal parameter between parentheses:
(a -> a + 2)(1)
(a -> b -> a + b)(1)(2)
Codeblocks:
Codeblocks can be used as expressions. A codeblock can contain both statements and expressions. The value the last statement evaluates to is what the entire codeblock evaluates to.
{ let a := 1 + 2; print a; 2; }
Conditional
if a < b then 1 else 2
Statements must always and with a semicolon.
Declaration:
All variables are lexial scoped inside codeblocks.
let a := 1;
let b := 1 + 2 * 3;
let c := {
let a := 1;
let b := 2;
a + b;
};
Assinging:
a := 42;
Expression statements:
All expressions can be used as a statement.
The result of any expression can be printed in the console with print:
print 3 / 2;
print 1 + 2 * 3;
print 3 - 9;
While
while a < 5 do {
print a;
};