Specification

This page illustrates how to create a language specification for use with the CBS IDE.

You should install the CBS IDE in Spoofax and install the CBS-beta repository in your file system before proceeding.

Create folders and links in the file system

1. Create a folder for your own collection of languages, e.g.: My-Languages
2. Choose a full name for your language (no spaces), e.g.: CBS-Demo
3. Create the folder CBS-Demo in My-Languages
4. Choose a short name for your language, e.g.: CD
5. Create the folder CD-cbs in CBS-Demo
6. Create the folder CD in CD-cbs
7. Create the folder CD-Start in CD
8. Create a symbolic link in CD-cbs to your copy of CBS-beta/Funcons-beta

Your resulting folder hierarchy should look something like this:¹

My-Languages
- CBS-Demo
  - CD-cbs
    - CD
      - CD-Start
    - Funcons-beta -> YOUR-PATH-TO/CBS-beta/Funcons-beta

CBS-beta
- ...
- Funcons-beta
- ...

Create a CBS language specification project in Spoofax

1. Make CD-cbs a general project
   1. Select File: New: Project...: Wizards: General: Project, click Next

   2. Project Name

      CD-cbs

      Location

      YOUR-PATH-TO/My-Languages/CBS-Demo/CD-cbs, click Finish

2. Add the Spoofax nature to the CD-cbs project:
   1. Right-click on the project
   2. Select Spoofax: Add Spoofax nature
3. Spoofax should now analyse your project (about 30 seconds), otherwise
   1. Check that the CBS language project has already been built
   2. Check that the Spoofax (meta) menu indicates that analysis is enabled
   3. Try cleaning the CD-cbs project
4. Expand the folder CD-cbs/Funcons-beta/Funcons-Index and open an editor on the file Funcons-Index.cbs
5. Check that:
   1. There are no parse errors
   2. CBS keywords and names are highlighted
   3. Command- or Control-hovering over names makes them hyperlinks
   4. Clicking a hyperlink opens an editor showing the declaration of the name

Specify your language

1. Check that the Spoofax (meta) menu indicates that analysis is currently enabled
2. Create a file named CD-Start.cbs in the CD-Start folder with the following contents:²

   Language "CBS-Demo"
       
   Syntax START:start ::= exp
       
   Semantics start[[ _:start ]] : =>values
   
   Rule start[[ E ]] =
     initialise-binding finalise-failing eval[[ E ]]
       
   Syntax E:exp ::= int
                  | id
                  | 'lambda' id '.' exp
                  | exp '(' exp ')'
                  | 'let' id '=' exp 'in' exp
                  | '(' exp ')'
       
   Semantics eval[[ _:exp ]] : => values
       
   Rule eval[[ N ]] = int[[ N ]]
       
   Rule eval[[ X ]] = bound id[[ X ]]
       
   Rule eval[[ 'lambda' X '.' E ]] =
     function closure
       scope( bind( id[[ X ]], given ), 
              eval[[ E ]] )
       
   Rule eval[[ E1 '(' E2 ')' ]] =
     apply( eval[[ E1 ]], eval[[ E2 ]] )
       
   Rule eval[[ 'let' X '=' E1 'in' E2 ]] =
       scope( bind( id[[ X ]], eval[[ E1 ]] ), 
              eval[[ E2 ]] )
       
   Rule eval[[ '(' E ')' ]] = eval[[ E ]]
       
       
   Lexis  N:int ::= ('0'-'9')+
       
   Semantics int[[ N:int ]] : => integers
               = decimal \"N\"
       
       
   Lexis  X:id  ::= ('a'-'z') ('a'-'z'|'0'-'9')*
       
   Semantics id[[ X:id ]] : => identifiers
               = \"X\"
   

3. Check that:
   1. There are no parse errors
   2. CBS keywords and names are highlighted
   3. Command- or Control-hovering over names makes them hyperlinks
   4. Clicking a hyperlink scrolls to the declaration of the name

You can now validate the above language specification by generating a translator from programs to funcons, and checking the outcomes of executing translations of test programs

Evolve a language and its specification

The following pages suggest various extensions of the language specified above.

You can add extensions to the specification of language syntax and semantics in CD-Start.cbs in any order. However, specification of syntactic grouping disambiguation is less modular; following the order shown below should ensure correct parsing of the suggested test programs when validating each extension.

In CBS, a language specification is not treated as a reusable component. You should invasively edit it when extending the specified language. If you commit each extension to a repository, you can compare commits to display their differences visually in Spoofax (the local history feature might also be used).

← →

Table of contents

• CD-1
• CD-2