1. Lesson Objectives
Aims
Understand Syntax Analysis

2. All languages (human and programming) have rules.
Syntax
All languages (human and programming) have rules.
Unlike English, for example, computers are totally unforgiving of bad grammar
“You’re a moron”
“Your a moron”
My a moron what?!

3. Syntax
Syntax is the grammar of a programming language
It is a set of rules that lines of code must adhere to in order to be “syntactically correct”
If a line of code does not adhere to any known rule, a syntax error is generated

4. Example

5. dimm chunder As Integer
Syntax Error
How does the compiler know this is a spelling error??
dimm chunder As Integer
How would this line of code be interpreted?

6. The syntax analyser will check for two things:
Spelling errors
Whether a token stream is valid and matches a given rule

7. The syntax analyser will use rules that are based on some form of logic
One such method is Backus Naur Form
This is a method of tightly defining atomic rules that cannot be misinterpreted
They are also recursive in nature

8. Once syntax has been verified, an Abstract Syntax Tree is produced
Why:
Unambiguous (tightly defined) data structure
Can only be read in one way
Removes any uncertainty about operator precedence

9. 2 * 3 + 4…. Which happens first?

10. Task
Find out and make notes on:
BNF – why is it used?
BNF – how are numbers represented (recursively(what is recursion??))
AST – what does a simple AST look like? What about for a common statement such as IF?

11. Review/Success Criteria
You should know:
What Syntax is
What role the syntax analysis stage plays in compilation
What will generate a syntax error
What an AST is
What BNF is and why it is useful in syntax parsing