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Using SableCC’s Visitor Pattern The main way of using SableCC’s visitor pattern is to define a class which extends DepthFirstAdapter. By over-riding the methods inAAssignStm or outAAssignStm etc. we can specify code to be executed when entering or leaving each node during a depth first traversal of the syntax tree. If we want to modify the order of traversal then we can over-ride caseAAssignStm etc. but this is often not necessary. The in and out methods return void, but the class provides HashTable in, out; which we can use to store types of expressions. 72
A SableCC Grammar with transformations SableCC specification of tokens: Package expression; Helpers digit = ['0' .. '9']; tab = 9; cr = 13; lf = 10; eol = cr lf | cr | lf; // This takes care of different platforms blank = (' ' | tab | eol)+; Tokens l_par = '('; r_par = ')'; plus = '+'; minus = '-'; mult = '*'; div = '/'; comma = ','; blank = blank; number = digit+; Ignored Tokens blank; 73
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Languages and Compilers (SProg og O
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Adding Actions by hand options { LO
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Attribute Grammars • Example: exp
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Attribute Grammars .expected_type
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Attribute Grammars • Let X 0 →
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Attribute Grammars and Practice •
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Back to Parsers - let us look at LR
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Hierarchy 15
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Bottom Up Parsers • Harder to imp
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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: Syntax Tree Classes for Prog For ea
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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