Beyond Syntax, Attributes Grammar - Compiler Construction - Lecture Slides, Slides of Compiler Construction

Download Beyond Syntax, Attributes Grammar - Compiler Construction - Lecture Slides and more Slides Compiler Construction in PDF only on Docsity!

Compiler

Construction

Lecture 31

2

Beyond Syntax

 These questions are part of

context-sensitive analysis

 Answers depend on values,

not parts of speech

 Answers may involve

computation

4

Beyond Syntax

 These questions are part of

context-sensitive analysis

 Answers depend on values,

not parts of speech

 Answers may involve

computation

5

Beyond Syntax

How can we answer these

questions?

 Use formal methods

• Context-sensitive

grammars

• Attribute grammars

7

Beyond Syntax

How can we answer these

questions?

 Use formal methods

• Context-sensitive

grammars

• Attribute grammars

8

Beyond Syntax

 Use ad-hoc techniques

• Symbol tables
• ad-hoc code

10

Attribute Grammars

 A CFG is augmented with a

set of rules

 Each symbol in the derivation

has a set of values or

attributes

 Rules specify how to compute

a value for each attribute

11

Attribute Grammars

 A CFG is augmented with a

set of rules

 Each symbol in the derivation

has a set of values or

attributes

 Rules specify how to compute

a value for each attribute

13

Attribute Grammars

derivation for “–1”

Number → Sign List

→ – List

→ – Bit

14

Attribute Grammars

For “-101”

Number → Sign List

→ Sign List Bit

→ Sign List 1

→ Sign List Bit 1

→ Sign List 0 1

→ Sign Bit 0 1

→ Sign 1 0 1

16

Attribute Grammars

 We will add rules to

compute decimal value of a

signed binary number

17

Attribute Grammars

Productions Attribution Rules

Number → Sign List List.pos ← 0 if Sign.neg then Number.val ← – List.val else Number.val ← List.val

Sign → + (^) Sign.neg ← false

Sign → – (^) Sign.neg ← true

19

Attribute Grammars

Productions Attribution Rules List 0 → List 1 Bit List 1 .pos ← List 0 .pos + 1 Bit.pos ← List 0 .pos List 0 .val ← List 1 .val + Bit.val

List → Bit Bit.pos ← List.pos List.val ← Bit.val

Bit → 0 Bit.val ← 0

Bit → 1 Bit.val ← 2 Bit.pos

20

Attribute Grammars

 Attributes are associated with

nodes in parse tree

 Rules are value assignments

associated with productions