CODEWITHSUNDEEP
phpregexparsingpseudocodelexer
CMR
CMR

Reputation: 1416

Converting pseudocode into usable (using regular expression?)

As part of the system I am writing, users can create their own custom Rules, to be run when certain events happen.

There are a set number of Objects they can use to create these rules, all of which have a set number of properties and methods:

list of objects

So as an example of a rule, we could say:

“if this unit award is ‘Distinction’ then set all the criteria on this unit to award ‘Achieved’”

IF UNIT.award equals “Distinction”
THEN UNIT.criteria.set_award(‘A’)

“else if this unit award is ‘Merit’ then set the award of any criteria on this unit whose name starts with either ‘P’ or ‘M’ to ‘Achieved’”

IF UNIT.award equals “Merit”
THEN UNIT.criteria.filter(‘starts’, ‘name’, ‘P’, ‘M’).set_award(‘A’)

“else if this unit award is ‘Pass then set the award of any criteria on this unit whose name starts with ‘P’ to ‘Achieved’”

IF UNIT.award equals “Merit”
THEN UNIT.criteria.filter(‘starts’, ‘name’, ‘P’).set_award(‘A’)

The problem I am having, is I am just not sure how to take that string of object, properties & methods, e.g. “UNIT.criteria.filter(‘starts’, ‘name’, ‘P’).set_award(‘A’)” and convert it into something usable.

The end result I’d like to convert the string to would be something along the lines of:

example result

So I can then convert that into the actual proper objects and return the relevant values or run the relevant methods.

Since there is only a set number of things I need to support (for now at least) and I don’t need anything complex like calculation support or variables, it seems overkill to create a Lexer system, so I was thinking of just using a regular expression to split all the sections.

So using the examples above, I could do a simple split on the “.” character, but if that character is used in a method parameter, e.g. “CRITERION.filter(‘is’, ‘name’, ‘P.1’)” then that screws it up completely.

I could use a less common character to split them, for example a double colon or something “::” but if for whatever reason someone puts that into a parameter it will still cause the same problem. I’ve tried creating a regular expression that splits on the character, only if it’s not between quotes, but I haven’t been able to get it to work.

So basically my question is: would a regular expression be the best way to do this? (If so, could anyone help me with getting it to ignore the specified character if it’s in a method). Or is there another way I could do this that would be easier/better?

Thanks.

Upvotes: 3

Views: 515

Answers (1)

Joeri
Joeri

Reputation: 2308

I'd think an ORM language like eloquent could do this for you.

But if I had to do this then first I'd split the IF THEN ELSE parts. Leaving:

  1. UNIT.award equals “Distinction”
  2. UNIT.criteria.filter(‘starts’, ‘name’, ‘P’, ‘M’).set_award(‘A’)

I'm guessing the "equals" could also be "not equals" or "greater" so... I'd split the first bit around that.

/(?'ident'[a-z.]*?) (?'expression'equals|greater) (?'compare'[0-9a-z\“\”]+)/gi

But an explode around 'equals' will do the same.

Then I'd explode the second part around the dots. Giving:

  1. UNIT
  2. criteria
  3. filter(a,b,c,d)
  4. set_ward(e)

Pop off the first 2 to get object and property and then a list of possible filters and actions.

But frankly I'd would develop a language that would not mix properties with actions and filters.

Something like:

IF object.prop EQUALS const|var 
THEN UPDATE object.prop 
WITH const|var [WHERE object.prop filter const|var [AND|OR const|var]]

Eloquent does it straight in php:

DB::table('users')
            ->where('id', 1)
            ->update(['votes' => 1]);

So maybe I'd do something like:

THEN object.prop->filter(a,b,c,d)->set('award','A')

This makes it easy to split actions around -> and properties around .

Anyway... I do my Regex on https://regex101.com/ Hope this helps.

Upvotes: 1

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