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Attribute Grammars • How are attribute values computed – If all attributes were inherited, the tree could be decorated in top-down order. – If all attributes were synthesized, the tree could be decorated in bottom-up order. – In many cases, both kinds of attributes are used, and it is some combination of top-down and bottom-up that must be used. – Top-down grammars (LL(k)) generally require inherited flows Copyright © 2004 Pearson Addison-Wesley. All rights reserved. 10
Attribute Grammars and Practice • The attribute grammar formalism is important – Succinctly makes many points clear – Sets the stage for actual, ad-hoc practice • The problems with attribute grammars motivate practice – Non-local computation – Need for centralized information (globals) • Advantages – Addresses the shortcomings of the AG paradigm – Efficient, flexible • Disadvantages – Must write the code with little assistance – Programmer deals directly with the details 11
Page 1 and 2: Languages and Compilers (SProg og O
Page 3 and 4: Adding Actions by hand options { LO
Page 5 and 6: Attribute Grammars • Example: exp
Page 7 and 8: Attribute Grammars .expected_type
Page 9: Attribute Grammars • Let X 0 →
Page 13 and 14: Back to Parsers - let us look at LR
Page 15 and 16: Hierarchy 15
Page 17 and 18: Bottom Up Parsers • Harder to imp
Page 19 and 20: Fundamental idea • Read through e
Page 21 and 22: Right derivations Sentence ::= Subj
Page 23 and 24: Bottom Up Parsers • All bottom up
Page 25 and 26: Model of an LR parser: stack sm xm
Page 27 and 28: The parse table • For every state
Page 29 and 30: Example - parse table ( ) $ S' S 0
Page 31 and 32: The resultat • Read the productio
Page 33 and 34: LR(0)-items Item : A production wit
Page 35 and 36: Goto(I,X) Describes the X-transitio
Page 37 and 38: LR(0)-parse table • state I with
Page 39 and 40: Shift-reduce-conflicts ( ) $ S' S 0
Page 41 and 42: Parser Conflict Resolution Most pro
Page 43 and 44: Parser Conflict Resolution Example:
Page 45 and 46: Parser Conflict Resolution Example:
Page 47 and 48: LR(0) vs. SLR • LR(0) - here we d
Page 49 and 50: LR(1) • Items are now pairs (A→
Page 51 and 52: Example 0: S' → S$ 1: S → V=E 2
Page 53 and 54: LR(1)-parse table x * = $ S E V x *
Page 55 and 56: LALR(1)-parse-table x * = $ S E V 1
Page 57 and 58: Enough background! • All of this
Page 59 and 60: JavaCUP: A LALR generator for Java
Page 61 and 62:
Java Cup Specification Structure ja
Page 63 and 64:
Ambiguous Grammar Error • If we e
Page 65 and 66:
Change the calc.cup terminal PLUS,
Page 67 and 68:
Steps to build a compiler with Sabl
Page 69 and 70:
SableCC output • The lexer packag
Page 71 and 72:
Syntax Tree Classes for Prog For ea
Page 73 and 74:
A SableCC Grammar with transformati
Page 75 and 76:
A SableCC Grammar with transformati
Page 77 and 78:
Advantages of SableCC • Automatic
Page 79 and 80:
Now let’s talk a bit about progra
Page 81:
Programming Language Design • The
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