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What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax...

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What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree
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Page 1: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

What am I?

while b != 0if a > ba := a − belseb := b − areturn a

AST ==AbstractSyntaxTree

Page 2: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators

Page 3: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Module Knowledge Areas• Types of translators and their use

• Lexical analysis

•Syntax analysis• Code generation and optimisation

• Library routines

Page 4: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Module Knowledge Areas

•Syntax analysis• describe what happens during syntax analysis

• explaining how errors are handled

So, you need to be able to:

• State what syntax analysis is• Describe the process of syntax analysis•   Explain the position of syntax analysis in the compilation process. You may

do this through a combination of diagrammatic and written evidence.

• Discuss the link between lexical analysis and syntax analysis with particular reference to the passing of lexical tokens to the syntax analyser

• Explain the part that syntax analysis plays in identifying errors in source code

Page 5: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

IF A>5 THEN A = A * 2ELSE A = A * 3A = A + 2

Explain the relationship between the table and the code (M)

Page 6: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

Explain the relationship between the table and the numbers

1 2 3 4 5 2 6 2 7 8 9 2 6 2 7 10 2 6 2 11 8

What is the significance of ‘2’ in the above sequence? (M)

Page 7: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

The journey

Phase Input Output

Lexer Sequence of characters

Sequence of tokens

Parser Sequence of tokens

Parse tree

Page 8: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

The Parser - Overview

• Performs syntax analysis• Imposes syntactic structure on a sentence

• Parse trees are used to expose the structure

• Parsers, accepts a string of tokens and builds a parse tree representing the program

Page 9: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

Symbol Table - Overview

• The symbol table is a data structure used by all phases of the compiler to keep track of user defined symbols and keywords

• During early phases (lexical and syntax analysis) symbols are discovered and put into the symbol table

• During later phases symbols are looked up to validate their usage

Page 10: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – Syntax Analysis

Symbol Table - Actions

• add a new name• add information for a name• access information for a name• determine if a name is present in the table• remove a name• revert to a previous usage for a name (close

a scope)

Page 11: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – AST

AST - Why

The syntax tree is a structure which can be guaranteed syntactically correct and only readable in one way - there are no issues with precedence of operations in how the program works

Page 12: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – AST

AST - How

What is happening here?

Simple operation of 2 * 3 in a symbolic layout

Page 13: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – AST

AST - How

Which are the operators and which are the operands?The operator is root and the operands are descendants of the root

Page 14: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – AST

AST - How

Consider the program statement 2 * 3 + 4

Create an AST to represent this

Page 15: What am I? while b != 0 if a > b a := a − b else b := b − a return a AST == Abstract Syntax Tree.

Translators – AST

AST - How

Which AST is correct for the statement

2 * 3 + 4?

Why? (M)


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