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Tree Generation

Tree Generation. Programming Language Principles Lecture 5. Prepared by Manuel E. Bermúdez, Ph.D. Associate Professor University of Florida. String-To-Tree Transduction. Can obtain derivation or abstract syntax tree. Tree can be generated top-down, or bottom-up.

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Tree Generation

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  1. Tree Generation Programming Language Principles Lecture 5 Prepared by Manuel E. Bermúdez, Ph.D. Associate Professor University of Florida

  2. String-To-Tree Transduction • Can obtain derivation or abstract syntax tree. • Tree can be generated top-down, or bottom-up. • We will show how to obtain • Derivation tree top-down • AST for the original grammar, bottom-up.

  3. Top-Down Generation of Derivation Tree • In each procedure, and for each alternative, write out the appropriate production AS SOON AS IT IS KNOWN

  4. Top-Down Generation of Derivation Tree (cont’d) proc S; {S → begin SL end → id := E; } case Next_Token of T_begin : Write(S →begin SL end); Read(T_begin); SL; Read(T_end);

  5. Top-Down Generation of Derivation Tree (cont’d) T_id : Write(S →id :=E;); Read(T_id); Read (T_:=); E; Read (T_;); otherwise Error end end;

  6. Top-Down Generation of Derivation Tree (cont’d) proc SL; {SL → SZ} Write(SL →SZ); S; Z; end; proc E; {E → TY} Write(E → TY); T; Y; end;

  7. Top-Down Generation of Derivation Tree (cont’d) proc Z; {Z →SZ → } case Next_Token of T_begin, T_id: Write(Z → SZ); S; Z; T_end: Write(Z → ); otherwise Error; end end;

  8. Top-Down Generation of Derivation Tree (cont’d) proc Y; {Y → +TY → } if Next_Token = T_+ then Write (Y → +TY); Read (T_+); T; Y; elseWrite (Y → ); end;

  9. Top-Down Generation of Derivation Tree (cont’d) proc T; {T → PX} Write (T →PX); P; X end; proc X;{X → *T → }

  10. Top-Down Generation of Derivation Tree (cont’d) if Next_Token = T_* then Write (X → *T); Read (T_*); T; elseWrite (X → ); end;

  11. Top-Down Generation of Derivation Tree (cont’d) proc P;{P → (E) → id } case Next_Token of T_(: Write (P → (E)); Read (T_(); E; Read (T_)); T_id: Write (P → id); Read (T_id); otherwise Error; end;

  12. Notes • The placement of the Write statements is obvious precisely because the grammar is LL(1). • Can build the tree “as we go”, or have it built by a post-processor.

  13. Input String: begin id := (id + id) * id; end Output: Example S → begin SL end SL → SZ S → id :=E; E → TY T → PX P → (E) E → TY T → PX P → id X → Y → +TY T → PX P → id X → Y → X → *T T → PX P → id X → Y → Z →

  14. Bottom-up Generation of the Derivation Tree • We could have placed the write statements at the END of each phrase, instead of the beginning. If we do, the tree will be generated bottom-up. • In each procedure, and for each alternative, write out the production A   AFTER  is parsed.

  15. Bottom-up Generation of the Derivation Tree (cont’d) proc S;{S → begin SL end → id := E; } case Next_Token of T_begin: Read (T_begin); SL; Read (T_end); Write (S → begin SL end); T_id: Read (T_id); Read (T_:=); E; Read (T_;); Write (S → id:=E;); otherwise Error; end;

  16. Bottom-up Generation of the Derivation Tree (cont’d) proc SL; {SL → SZ} S; Z; Write(SL → SZ); end; proc E; {E → TY} T; Y; Write(E → TY); end;

  17. Bottom-up Generation of the Derivation Tree (cont’d) proc Z; {Z → SZ → } case Next_Token of T_begin, T_id: S; Z; Write(Z → SZ); T_end: Write(Z → ); otherwise Error; end end;

  18. Bottom-up Generation of the Derivation Tree (cont’d) proc Y; {Y → +TY → } if Next_Token = T_+ then Read (T_+); T; Y; Write (Y → +TY); elseWrite (Y → ); end;

  19. Bottom-up Generation of the Derivation Tree (cont’d) proc T; {T → PX } P; X; Write (T → PX) end; proc X;{X → *T → } if Next_Token = T_* then Read (T_*); T; Write (X → *T); elseWrite (X → ); end

  20. Bottom-up Generation of the Derivation Tree (cont’d) proc P;{P → (E) → id } case Next_Token of T_(: Read (T_(); E; Read (T_)); Write (P → (E)); T_id: Read (T_id); Write (P → id); otherwise Error; end;

  21. Notes • The placement of the Write statements is still obvious. • The productions are emitted as procedures quit, not as they start.

  22. Notes (cont’d) • Productions emitted in reverse order, i.e., the sequence of productions must be used in reverse order to obtain a right-most derivation. • Again, can built tree “as we go” (need stack of trees), or later.

  23. Input String: begin id := (id + id) * id; end Output: Example P → id X → T → PX P → id X → T → PX Y → Y → +TY E → TY P → (E) P → id X → T → PX X → *T T → PX Y → E → TY S → id:=E; Z → SL → SZ S → begin SL end

  24. Tree Generation Programming Language Principles Lecture 5 Prepared by Manuel E. Bermúdez, Ph.D. Associate Professor University of Florida

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