I-Beams in Dyalog APL


This section adds more detail to the I-Beam functionality that has been added to Dyalog APL 12.1.

As ever, please remember the caveat that appears in the Language Guide:

Warning: Although documentation is provided for I-Beam functions, any service provided using I-Beam should be considered as “experimental” and subject to change – without notice - from one release to the next. Any use of I-Beams in applications should therefore be carefully isolated in cover-functions that can be adjusted if necessary.

200: Syntax Colouring

The Language Reference details the use of 200⌶ with function or operator definitions:

However, this I-Beam has been extended to include Namespaces, Classes and Interfaces, using the following syntax:

where type is one of the following:


Object type


Function (use ⎕nr)







Since any vector of character vectors could be passed to 200⌶, the type is used to indicate to the interpreter what it should base its analysis on. So, for example if you run

then the namespace-specific tags will appear as 243 - "Mismatched control structure"; you can't have a :Namespace in a function definition !

Whereas if you run

then the :Namespace element will appear as a valid one (177).

The attached file lists all of the syntactic colour elements. Note that this list is very version-specific; this list was generated on 2009-11-20 for V12.1, and may be extended, reduced or removed altogether in future versions.

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IBeamsWithDyalog (last edited 2012-07-18 08:51:47 by KaiJaeger)