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Bottom Up Parsers: Overview of Algorithms • LR(0) : The simplest algorithm, theoretically important but rather weak (not practical) • SLR : An improved version of LR(0), more practical but still rather weak. • LR(1) : LR(0) algorithm with extra lookahead token. – very powerful algorithm. Not often used because of large memory requirements (very big parsing tables) • LALR : “Watered down” version of LR(1) – still very powerful, but has much smaller parsing tables – most commonly used algorithm today 18
Fundamental idea • Read through every construction and recognize the construction at the end • LR: – Left – the string is read from left to right – Right – we get a right derivation • The parse tree is build from bottom up 19
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 and 10: Attribute Grammars • Let X 0 →
Page 11 and 12: Attribute Grammars and Practice •
Page 13 and 14: Back to Parsers - let us look at LR
Page 15 and 16: Hierarchy 15
Page 17: Bottom Up Parsers • Harder to imp
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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