[Newbies] Re: [on] how to match partial regexes? how to match and delete string prefixes?

[Zulq Alam]

Hi Oscar,

Oscar Nierstrasz wrote:
> 
> Hi Folks,
> 
> Is there a way ask a regex if it matches any part of a string?  matches: 
> wants an exact match, and matchesPrefix: clearly only matches a prefix.  
> The best I found was to abuse matchesIn: and check the size of the 
> response, but this is not very clean.

Have a look at #search: as I think this will help you.

> ---
> 
> A second question: I would like to strip a string prefix if it matches.  
> Since this is a literal string, I should not need regexes.  But I cannot 
> find a nice existing method to do this.  With regexes I must escape all 
> special regex chars:

I can't think of anything off the top of my head but the great thing 
about smalltalk is you can easily add what you need. For example, you 
could use #beginsWith: when adding a method to String.

copyReplacePrefix: prefix with: replacement
   self beginsWith: prefix
     ifTrue: [^ replacement , (self copyFrom: prefix size to: self size)]
   ^ self

Then you will be able to do:

'abracadabra' copyReplacePrefix: 'abra' with: ''

Next step would be to write a few unit tests and then attach both as to 
an enhancement request at http://bugs.squeak.org.

> 
> aliasesAsRegexes
>     aliasesAsRegexes ifNil: [
>     aliasesAsRegexes := aliases collect: [:alias |
>         alias := '\/' asRegex copy: alias replacingMatchesWith: '\/'.
>         alias := '\~' asRegex copy: alias replacingMatchesWith: '\~'.
>         alias := '\:' asRegex copy: alias replacingMatchesWith: '\:'.
>         alias := '\.' asRegex copy: alias replacingMatchesWith: '\.'.
>         alias asRegex
>         ]].
>     ^ aliasesAsRegexes
> 

I don't think /, ~ or : have any special meaning so why do you need to 
escape them? Even if you did, a better way might be to do:

alias
   copyWithRegex: '[/~:.]'
   matchesTranslatedUsing: [:ea | '\' , ea]

But if you're just replacing '.' then you can use:

alias copyReplaceAll: '.' with: '\.'

Hope this helps.

Zulq