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Error trapping with Dyalog APL: Difference between revisions
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Error trapping with Dyalog APL (view source)
Revision as of 15:23, 20 November 2019
, 15:23, 20 November 20196 revisions imported: Migrate from miraheze
Miraheze>Adám Brudzewsky (Created page with "To write bug-free code in a complex system and to forecast all errors is impossible. Therefore, implementing some kind of error trapping in an application which is supposed to...") |
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=== Restarting the application === | === Restarting the application === | ||
For reasons explained in a minute we now have to define the “Restart the application” procedure. For this, for the first time we do not use the <source lang=apl inline>'E' statement but the <source lang=apl inline>'C'</source> statement. The ''C'' is short for ''Cut back''. This instructs APL to cut the status indicator back to the level where <source lang=apl inline>⎕TRAP</source> '''is localized''' – that is not necessarily where it was set – and execute the expression in the 3rd argument there. However, if <source lang=apl inline>⎕TRAP</source> is not localized at all, i.e. it is in the workspace, the status indicator is cut back completely and the expression is executed in the workspace. | For reasons explained in a minute we now have to define the “Restart the application” procedure. For this, for the first time we do not use the <source lang=apl inline>'E'</source> statement but the <source lang=apl inline>'C'</source> statement. The ''C'' is short for ''Cut back''. This instructs APL to cut the status indicator back to the level where <source lang=apl inline>⎕TRAP</source> '''is localized''' – that is not necessarily where it was set – and execute the expression in the 3rd argument there. However, if <source lang=apl inline>⎕TRAP</source> is not localized at all, i.e. it is in the workspace, the status indicator is cut back completely and the expression is executed in the workspace. | ||
<source lang=apl> | <source lang=apl> | ||
⎕TRAP,←⊂(#.Events.RestartAppl 'C' '→∆Restart') | ⎕TRAP,←⊂(#.Events.RestartAppl 'C' '→∆Restart') | ||
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The best idea, however, is to use <source lang=apl inline>⎕NEXISTS</source> to check the file for already being created. In general it is a good idea to use error trapping only for extraordinary problems. | The best idea, however, is to use <source lang=apl inline>⎕NEXISTS</source> to check the file for already being created. In general it is a good idea to use error trapping only for extraordinary problems. | ||
=== <source lang=apl inline>⎕SIGNAL</source> === | === The <source lang=apl inline>⎕SIGNAL</source> system function === | ||
Note that an event which is <source lang=apl inline>⎕SIGNAL</source>led can be intercepted with <source lang=apl inline>⎕TRAP</source> but not <source lang=apl inline>:Trap</source> | Note that an event which is <source lang=apl inline>⎕SIGNAL</source>led can be intercepted with <source lang=apl inline>⎕TRAP</source> but not <source lang=apl inline>:Trap</source> | ||
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== Code == | == Code == | ||
{{Collapse|The below workspace contains all the code needed to implement the ideas discussed above.|<source lang=apl> | |||
The below workspace contains all the code needed to implement the ideas discussed above. | |||
<source lang=apl> | |||
(⎕IO ⎕ML ⎕WX)←1 1 3 | (⎕IO ⎕ML ⎕WX)←1 1 3 | ||
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:EndNamespace | :EndNamespace | ||
</source> | </source> | ||
}} | |||
[[Category:Tutorials]] | |||