Lesson Objectives Aims Understand Syntax Analysis

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?!

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

Example

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?

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

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

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

2 * 3 + 4…. Which happens first?

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?

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