Getting to Know Decaf Goals for Today: Get acquainted with the Decaf language Get experience with ASTs

The Decaf Language Activity #1: With a partner: Using the Decaf language specification handout, and comparing with either Java or C++: 1. Create a list of similarities between Decaf and Java/C++ 2. Create a list of differences between Decaf and Java/C++ Be ready to discuss your results, and also turn in your written listings with your names on it at the end of the activity. Timing: 20 minutes – reading and list creation 15 minutes – reporting out – charts on the board, discussion

Abstract Syntax Trees What are they? Give example for some strings of the grammar: E -> E + T | E – T | T T -> T * a | T / a | a

Building an AST during Parsing S -> E{ $$ = $1; root = $$; } E -> E + T{ $$ = makenode( ‘ + ’, $1, $3);} // E is $1, - is $2, T is $3 E -> E - T{ $$ = makenode( ‘ - ’, $1, $3);} E -> T{ $$ = $1;} // $$ is top of stack T -> ( E ){ $$ = $2;} T -> id{ $$ = makeleaf( ‘ idnode ’, $1);} T -> num{ $$ = makeleaf( ‘ numnode ’, $1);} Consider parsing 4 + ( x - y ) state semantic value Parsing Stack S 4 num S

Getting to know the Decaf Compiler AST Representation Consider the Decaf program: void main() { Print("hello world"); }

The Decaf Parser Output Program: 1 FnDecl: (return type) Type: void 1 Identifier: main (body) StmtBlock: PrintStmt: 2 (args) StringConstant: "hello world"

Practice with Decaf ASTs Activity 2: With a partner, draw an AST for the Decaf program using the grammar from the Decaf specification language handout: class Cow { int height; bool isSpotted; void Moo() { Print ( this.height, " ", isSpotted, "\n" ); } void main() { Cow betsy; betsy = New(Cow); betsy.Moo(); }

The Decaf Parser Output Program: 1 ClassDecl: 1 Identifier: Cow 2 VarDecl: Type: int 2 Identifier: height 3 VarDecl: Type: bool 3 Identifier: isSpotted 4 FnDecl: (return type) Type: void 4 Identifier: Moo (body) StmtBlock: PrintStmt: 5 (args) FieldAccess: 5 This: 5 Identifier: height 5 (args) StringConstant: " " 5 (args) FieldAccess: 5 Identifier: isSpotted 5 (args) StringConstant: "\n" 10 FnDecl: (return type) Type: void 10 Identifier: main (body) StmtBlock: 11 VarDecl: 11 NamedType: 11 Identifier: Cow 11 Identifier: betsy 12 AssignExpr: 12 FieldAccess: 12 Identifier: betsy 12 Operator: = 12 NewExpr: 12 NamedType: 12 Identifier: Cow 13 Call: 13 FieldAccess: 13 Identifier: betsy 13 Identifier: Moo