Lesson 31 of 55
10 mins readSymbols & Expression Objects (AST)
In Plain English
In Julia, code is data (Homoiconicity). Julia programs can parse, construct, and transform Julia expressions at compile time using Symbol and Expr objects.
Deep Dive: How It Works
Symbol: An interned identifier created with a colon prefix (e.g. :x, :my_var). Symbols represent variable names in the syntax tree.
Expr: Represents an expression node in the AST with fields: head (Symbol), args (Vector of sub-expressions), and optional type.
Meta.parse: Parses a Julia code string into an Expr object ready for metaprogramming.
Core Rules to Remember
Homoiconicity (Code is Data): Julia code is represented as native Julia data structures (Expr and Symbol).
Meta.parse(): Converts a string of code into an inspectable expression tree.
Live Interactive Example
Hit Run Code to see it liveExpression Inspection and AST Structure
Python 3.12
1
2
3
4
5
6
7
8
9
10
11
12
13
Output Console
Click "Run Code" to view the rendered output.
How it works: The parser produced a :call head with the :+ symbol and two operand arguments.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Parse and Inspect Expression
- Parse `"x^2 + 1"` using `Meta.parse("x^2 + 1")`.
- Print `"Head: $(ex.head)"`.
1
2
Sandbox Output
Click "Run & Check" to test your solution.
Finished reading and practicing?
Mark this lesson as completed to update your course progress.