1 / 20

The TXL Programming Language (4)

The TXL Programming Language (4). Mariano Ceccato FBK - Fondazione Bruno Kessler ceccato@fbk.eu. Announcement. No class: on March 26 th and 27 th Room change (107) on April 2 nd and 3 rd March 12 th and 13 th. Working with Global Variables.

rogerwhite
Download Presentation

The TXL Programming Language (4)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The TXL Programming Language (4) Mariano Ceccato FBK - Fondazione Bruno Kessler ceccato@fbk.eu

  2. Announcement • No class: on March 26th and 27th • Room change (107) on • April 2nd and 3rd • March 12th and 13th

  3. Working with Global Variables • Global variables are a rich and powerful feature that can be used for many distinct purposes, including: - global tables. - multiple results from a rule. - “deep” parameters. - “message-passing” communication between rules in a rule set (e.g, avoiding interference).

  4. Setting Global Table • Global tables can be set up using an export clause before the replace clause in the main rule of a program. Example: function main export Table [repeat table_entry] “Veggie” -> “Cabbage” “Fruit” -> “Apple” “Fruit” -> “Orange” replace [program] P [program] by P [R1] end function define table_entry [stringlit] -> [stringlit] end define

  5. Adding Table Entry • Global tables can be modified by exporting a new binding for the table based on the imported original binding. Example: function addTableEntry import Table [repeat table_entry] … construct newEntry [table_entry] “Veggie” -> “XXX” export Table Table [. newEntry] … end function

  6. Searching in a Table • Global tables can be easily queried using searching deconstructors. deconstruct * [table_entry] Table Kind [stringlit] -> “Orange” Example: • The binding for “Kind” will be the [stringlit] “Fruit”. If no match were to be found, then the deconstructor would fail.

  7. Avoiding interference between rules function shiftByOne export Flag [id] ‘not_found replace [number] N [number] by N [replaceOneByTwo] [replaceTwoByThree] end function function replaceOneByTwo replace [number] 1 export Flag ‘found by 2 end function We want: 1 ---> 2 ---> 3 2 ---> 3 function replaceTwoByThree import Flag [id] deconstruct Flag ‘not_found replace [number] 2 by 3 end function

  8. Remarks • Transformation of a list of contiguos if-statements in a case-statement. 1) The rule “transformTwoCases” is necessary. 2) It is not possible create a sequence [repeat T] in this way: - L elem with L [repeat T] and elem [T] - L L’ with L [repeat T] and L’ [repeat T] The Built-in function L [. elem] (or L [. L’]) can be used. If x>1 then … If x<1 then … case … endCase case … endCase case … endCase case … endCase

  9. Exercises • Adding to the Expr-language the construct ‘let’. • Extending the Calculator.txl at the ‘Let-Expr-language’. • - without global-variables (similar to pag. 19 slides 2) • - using global-variables let begin x = 1; y = 2; end x+y+1. [number] The output of Calculator.txl on the example will be 4.

  10. Homework • Extending the right part of the ‘let-declarations’ ([expression] • instead of [number]). • Extending the Calculator.txl at the ‘New-Let-Expr-language’. • - without global-variables • - using global-variables let begin x = 2; y = 1+x; x = 3 end x+y. The output of Calculator.txl on the example will be 6.

  11. Counting items in TXL • TXL can be used for counting items (i.e. LOCs, number of cycles, etc.). For example: given a tag-language counting the number of tags and end-tags. <a> uno <b> due </b> tags: 2 end Tags: 1

  12. % Tags grammar define program [repeat element] end define define element [Tag] | [endTag] | [id] end define define Tag < [id] > end define define endTag </ [id] > end define % Count number of tag and end-tag function main replace [program] P [program] construct ListTags [repeat Tag] _ [^ P] construct NumberTags [number] _ [countTag each ListTags] [printf] by end function R1 [^ X1] Replace R1 of type [repeat T] with a sequence consisting of every subtree of type [T] contained in X1.

  13. function countTag A [Tag] replace [number] N [number] by N [+ 1] end function function printf match [number] N [number] construct PrintObj [number] N [print] end function print is a built-in function!

  14. Using attributes TXL allows a grammar definition to have attributes associated with it: • Attributes act like optional non-terminals, but normally do not appear in the output (txl –attr force the print of all attributes). • Attributes may be added to the parse tree during transformations. • Attributes are denotated in the grammar by the nonterminal modifier attr.

  15. define type ‘int | ‘string end define define typed_id [id] [attr type] end define function InferType expr [expression] replace [typed_id] Id [id] deconstruct expr f [number] op [operator] s [number] by Id ‘int end function The attribute ‘type’ is Optional.

  16. Remark • Several functions (or rules) may be applied to a scope • in succession. For example: X [f][g][h] (the meaning is: h(g(f(X))) )

  17. Exercises (1) • Adding to the commands-language the statements: • - ‘goto’ • - ‘while’ • and the ‘labels’ (in optional way). f := 0; A_0: if x>n goto B_3; x := x –1; f := f * x; goto A_0; B_3: print f f := 0; while x <=n do x := x –1; f := f * x; endwhile print f

  18. Exercises (2) • Count the number of line of code in the input program. • Implement the ‘goto elimination’ transformation (before, think of ‘goto patterns’ that can be transformed in ‘while patterns’). f := 0; A_0: if x>n goto B_3; x := x –1; f := f * x; goto A_0; B_3: print f f := 0; while x <=n do x := x –1; f := f * x; endwhile print f goto elimination ‘1’

  19. Homework • Counting the number of line of code that contains the • ‘goto’ statement. • 2. Inferring the type of a variable from expressions • (using attributes). Example: - y: = 4; --> y: int - x := 5 +y; --> x: int

  20. All the exercises: • Ambiguous expr-language (+, *, -, /) • simplyfing rules (eg, remove-pus-zero) • Non-ambiguous expr-language • Adapt the simplifying rules • Implementing the Calculator.txl. • Add exponential Exp(x, n). to expr-grammar • Solve in syntax way: Exp(2, 3) --> 2*2*2 • Solve in semantic way: recursive function that substitute at Exp(x, n) the correct value. • “Commands-language” where commands can be: • assignments [id] := [expr]; • declarations const [id] = [number]; • Implement “resolveConstants” • Add to the “commands language”: • If [cond] then [repeat statement] endIf • Case [repeat caseEntry] endCase • [cond] -> [statement] • Transform a list of contiguos “if-statements” in a case-statement • Transform a case-statement in a list of contiguos “if-statements”. • Add the construct ‘let’. to the Expr-language • Extend the Calculator.txl at the ‘Let-Expr-language’. • without global-variables (similar to pag. 19 slides 2) • using global-variables • Extend ‘let-declarations’ • right part ([expression] instead of [number]). • Calculator for New-Let-Expr-language • without global-variables • using global-variables • Add “goto” , “while” and “labels” to command-language • Count statements • Implement goto-elimination • Conuntgoto statements • Type inferences

More Related