I'd like to write an app, my_app, that takes a list of named options and a list of filenames from the cmdline, e.g.,
% my_app --arg_1 arg_1_value filename_1 filename_2
The filenames are the last args and are not associated with any named options.
From the cmdline parsers, e.g., flag in Golang, that I've worked, it seems that the parsers will only extract the args that are configured, and that I'd need to identify the list of filenames manually by walking thru the original argv[] list.
I'd like to ask if there are parsers (or their options that I may have overlooked) that can also extract those filenames, or they only return the unprocessed args, and therefore, I could assume that these are the filenames.
The Golang flag module makes the trailing arguments available as the slice flag.Args, which is the trailing part of os.Args.
That's a pretty typical way for command-line argument parsers to work, although the details will vary according to language. The standard C library argument parser, fir example, provides the global optind, which is the index in argv of the first non-flag argument.
I am playing around with Tatsu to implement a parser for a language used in the semiconductor industry. This language requires that variables be defined before usage. So for example:
SignalGroup { A: In; B: Out};
Pattern {
V {A=1, B=1 }
V {A=1, B=0 }
};
In this case, the SignalGroup block must come before the Pattern block. How do I enforce/implement this "ordering" when writing the grammer in TatSu?
Although for some languages it is possible to write grammars that verify if the same symbol appears on different places, the grammars usually end up being too complicated to be useful.
Compilers (translators) are usually implemented with separate lexical, syntactical, and semantic analyzer components. There are several reasons for that:
Each component is so well focused that it is clearer and easier to write.
Each component is very efficient
The most common errors (which are exactly lexical, syntactical, and semantic) can be reported earlier
With those components in mind, checking if a symbol has ben previously defined belongs to the semantic (meaning) aspect of the program, and the way to check is to keep a symbol table that is filled when the definition parts of the input are being parsed, and queried on the use parts of the input are being parsed.
In TatSu in particular the different components are well separated, yet run in parallel. For your requirement you just need to use the simplest grammar that allows for the semantic actions that store and query the symbols. By raising FailedSemantics from within semantic actions, any semantic errors will be reported exactly as the lexical and syntactical ones so the user doesn't have to think about which component flagged each error.
If you use the Python parser generation in TatSu, the translator will generate the skeleton of a semantic actions class as part of the output.
I have this .bib file for reference management while writing my thesis in LaTeX:
#article{garg2017patch,
title={Patch testing in patients with suspected cosmetic dermatitis: A retrospective study},
author={Garg, Taru and Agarwal, Soumya and Chander, Ram and Singh, Aashim and Yadav, Pravesh},
journal={Journal of Cosmetic Dermatology},
year={2017},
publisher={Wiley Online Library}
}
#article{hauso2008neuroendocrine,
title={Neuroendocrine tumor epidemiology},
author={Hauso, Oyvind and Gustafsson, Bjorn I and Kidd, Mark and Waldum, Helge L and Drozdov, Ignat and Chan, Anthony KC and Modlin, Irvin M},
journal={Cancer},
volume={113},
number={10},
pages={2655--2664},
year={2008},
publisher={Wiley Online Library}
}
#article{siperstein1997laparoscopic,
title={Laparoscopic thermal ablation of hepatic neuroendocrine tumor metastases},
author={Siperstein, Allan E and Rogers, Stanley J and Hansen, Paul D and Gitomirsky, Alexis},
journal={Surgery},
volume={122},
number={6},
pages={1147--1155},
year={1997},
publisher={Elsevier}
}
If anyone wants to know what bib file is, you can find it detailed here.
I'd like to parse this with Perl 6 to extract the key along with the title like this:
garg2017patch: Patch testing in patients with suspected cosmetic dermatitis: A retrospective study
hauso2008neuroendocrine: Neuroendocrine tumor epidemiology
siperstein1997laparoscopic: Laparoscopic thermal ablation of hepatic neuroendocrine tumor metastases
Can you please help me to do this, maybe in two ways:
Using basic Perl 6
Using a Perl 6 Grammar
TL;DR
A complete and detailed answer that does just exactly as #Suman asks.
An introductory general answer to "I want to parse X. Can anyone help?"
A one-liner in a shell
I'll start with terse code that's perfect for some scenarios[1], and which someone might write if they're familiar with shell and Raku basics and in a hurry:
> raku -e 'for slurp() ~~ m:g / "#article\{" (<-[,]>+) \, \s+
"title=\{" (<-[}]>+) \} / -> $/ { put "$0: $1\n" }' < derm.bib
This produces precisely the output you specified:
garg2017patch: Patch testing in patients with suspected cosmetic dermatitis: A retrospective study
hauso2008neuroendocrine: Neuroendocrine tumor epidemiology
siperstein1997laparoscopic: Laparoscopic thermal ablation of hepatic neuroendocrine tumor metastases
Same single statement, but in a script
Skipping shell escapes and adding:
Whitespace.
Comments.
► use tio.run to run the code below
for slurp() # "slurp" (read all of) stdin and then
~~ m :global # match it "globally" (all matches) against
/ '#article{' (<-[,]>+) ',' \s+ # a "nextgen regex" that uses (`(...)`) to
'title={' (<-[}]>+) '}' / # capture the article id and title and then
-> $/ { put "$0: $1\n" } # for each article, print "article id: title".
Don't worry if the above still seems like pure gobbledygook. Later sections explain the above while also introducing code that's more general, clean, and readable.[2]
Four statements instead of one
my \input = slurp;
my \pattern = rule { '#article{' ( <-[,]>+ ) ','
'title={' ( <-[}]>+ ) }
my \articles = input .match: pattern, :global;
for articles -> $/ { put "$0: $1\n" }
my declares a lexical variable. Raku supports sigils at the start of variable names. But it also allows devs to "slash them out" as I have done.
my \pattern ...
my \pattern = rule { '#article{' ( <-[,]>+ ) ','
'title={' ( <-[}]>+ ) }
I've switched the pattern syntax from / ... / in the original one-liner to rule { ... }. I did this to:
Eliminate the risk of pathological backtracking
Classic regexes risk pathological backtracking. That's fine if you can just kill a program that's gone wild, but click the link to read how bad it can get! 🤪 We don't need backtracking to match the .bib format.
Communicate that the pattern is a rule
If you write a good deal of pattern matching code, you'll frequently want to use rule { ... }. A rule eliminates any risk of the classic regex problem just described (pathological backtracking), and has another superpower. I'll cover both aspects below, after first introducing the adverbs corresponding to those superpowers.
Raku regexes/rules can be (often are) used with "adverbs". These are convenient shortcuts that modify how patterns are applied.
I've already used an adverb in the earlier versions of this code. The "global" adverb (specified using :global or its shorthand alias :g) directs the matching engine to consume all of the input, generating a list of as many matches as it contains, instead of returning just the first match.
While there are shorthand aliases for adverbs, some are used so repeatedly that it's a lot tidier to bundle them up into distinct rule declarators. That's why I've used rule. It bundles up two adverbs appropriate for matching many data formats like .bib files:
:ratchet (alias :r)
:sigspace (alias :s)
Ratcheting (:r / :ratchet) tells the compiler that when an "atom" (a sub-pattern in a rule that is treated as one unit) has matched, there can be no going back on that. If an atom further on in the pattern in the same rule fails, then the whole rule immediately fails.
This eliminates any risk of the "pathological backtracking" discussed earlier.
Significant space handling (:s / :sigspace) tells the compiler that an atom followed by literal spacing that is in the pattern indicates that a "token" boundary pattern, aka ws should be appended to the atom.
Thus this adverb deals with tokenizing. Did you spot that I'd dropped the \s+ from the pattern compared to the original one in the one-liner? That's because :sigspace, which use of rule implies, takes care of that automatically:
say 'x#y x # y' ~~ m:g:s /x\#y/; # (｢x#y｣) <-- only one match
say 'x#y x # y' ~~ m:g /x \# y/; # (｢x#y｣) <-- only one match
say 'x#y x # y' ~~ m:g:s /x \# y/; # (｢x#y｣ ｢x # y｣) <-- two matches
You might wonder why I've reverted to using / ... / to show these two examples. Turns out that while you can use rule { ... } with the .match method (described in the next section), you can't use rule with m. No problem; I just used :s instead to get the desired effect. (I didn't bother to use :r for ratcheting because it makes no difference for this pattern/input.)
To round out this dive into the difference between classic regexes (which can also be written regex { ... }) and rule rules, let me mention the other main option: token. The token declarator implies the :ratchet adverb, but not the :sigspace one. So it also eliminates the pathological backtracking risk of a regex (or / ... /) but, just like a regex, and unlike a rule, a token ignores whitespace used by a dev in writing out the rule's pattern.
my \articles = input .match: pattern, :global
This line uses the method form (.match) of the m routine used in the one-liner solution.
The result of a match when :global is used is a list of Match objects rather than just one. In this case we'll get three, corresponding to the three articles in the input file.
for articles -> $/ { put "$0: $1\n" }
This for statement successively binds a Match object corresponding to each of the three articles in your sample file to the symbol $/ inside the code block ({ ... }).
Per Raku doc on $/, "$/ is the match variable, so it usually contains objects of type Match.". It also provides some other conveniences; we take advantage of one of these conveniences related to numbered captures:
The pattern that was matched earlier contained two pairs of parentheses;
The overall Match object ($/) provides access to these two Positional captures via Positional subscripting (postfix []), so within the for's block, $/[0] and $/[1] provide access to the two Positional captures for each article;
Raku aliases $0 to $/[0] (and so on) for convenience, so most devs use the shorter syntax.
Interlude
This would be a good time to take a break. Maybe just a cuppa, or return here another day.
The last part of this answer builds up and thoroughly explains a grammar-based approach. Reading it may provide further insight into the solutions above and will show how to extend Raku's parsing to more complex scenarios.
But first...
A "boring" practical approach
I want to parse this with Raku. Can anyone help?
Raku may make writing parsers less tedious than with other tools. But less tedious is still tedious. And Raku parsing is currently slow.
In most cases, the practical answer when you want to parse well known formats and/or really big files is to find and use an existing parser. This might mean not using Raku at all, or using an existing Raku module, or using an existing non-Raku parser in Raku.
A suggested starting point is to search for the file format on modules.raku.org or raku.land. Look for a publicly shared parsing module already specifically packaged for Raku for the given file format. Then do some simple testing to see if you have a good solution.
At the time of writing there are no matches for 'bib'.
Even if you don't know C, there's almost certainly a 'bib' parsing C library already available that you can use. And it's likely to be the fastest solution. It's typically surprisingly easy to use an external library in your own Raku code, even if it's written in another programming language.
Using C libs is done using a feature called NativeCall. The doc I just linked may well be too much or too little, but please feel free to visit the freenode IRC channel #raku and ask for help. (Or post an SO question.) We're friendly folk. :)
If a C lib isn't right for a particular use case, then you can probably still use packages written in some other language such as Perl, Python, Ruby, Lua, etc. via their respective Inline::* language adapters.
The steps are:
Install a package (that's written in Perl, Python or whatever);
Make sure it runs on your system using a compiler of the language it's written for;
Install the appropriate Inline language adapter that lets Raku run packages in that other language;
Use the "foreign" package as if it were a Raku package containing exported Raku functions, classes, objects, values, etc.
(At least, that's the theory. Again, if you need help, please pop on the IRC channel or post an SO question.)
The Perl adapter is the most mature so I'll use that as an example. Let's say you use Perl's Text::BibTex packages and now wish to use Raku with that package. First, setup it up as it's supposed to be per its README. Then, in Raku, write something like:
use Text::BibTeX::BibFormat:from<Perl5>;
...
#blocks = $entry.format;
Explanation of these two lines:
The first line is how you tell Raku that you wish to load a Perl module.
(It won't work unless Inline::Perl5 is already installed and working. But it should be if you're using a popular Raku bundle. And if not, you should at least have the module installer zef so you can run zef install Inline::Perl5.)
The last line is just a mechanical Raku translation of the #blocks = $entry->format; line from the SYNOPSIS of the Perl package Text::BibTeX::BibFormat.
A Raku grammar / parser
OK. Enough "boring" practical advice. Let's now try have some fun creating a grammar based Raku parser good enough for the example from your question.
► use glot.io to run the code below
unit grammar bib;
rule TOP { <article>* }
rule article { '#article{' $<id>=<-[,]>+ ','
<kv-pairs>
'}'
}
rule kv-pairs { <kv-pair>* % ',' }
rule kv-pair { $<key>=\w* '={' ~ '}' $<value>=<-[}]>* }
With this grammar in place, we can now write something like:
die "Use CommaIDE?" unless bib .parsefile: 'derm.bib';
for $<article> -> $/ { put "$<id>: $<kv-pairs><kv-pair>[0]<value>\n" }
to generate exactly the same output as the previous solutions.
When a match or parse fails, by default Raku just returns Nil, which is, well, rather terse feedback.
There are several nice debugging options to figure out what's going on with a regex or grammar, but the best option by far is to use CommaIDE's Grammar-Live-View.
If you haven't already installed and used Comma, you're missing one of the best parts of using Raku. The features built in to the free version of Comma ("Community Edition") include outstanding grammar development / tracing / debugging tools.
Explanation of the 'bib' grammar
unit grammar bib;
The unit declarator is used at the start of a source file to tell Raku that the rest of the file declares a named package of code of a particular type.
The grammar keyword specifies a grammar. A grammar is like a class, but contains named "rules" -- not just named methods, but also named regexs, tokens, and rules. A grammar also inherits a bunch of general purpose rules from a base grammar.
rule TOP {
Unless you specify otherwise, parsing methods (.parse and .parsefile) that are called on a grammar start by calling the grammar's rule named TOP (declared with a rule, token, regex, or method declarator).
As a, er, rule of thumb, if you don't know if you should be using a rule, regex, token, or method for some bit of parsing, use a token. (Unlike regex patterns, tokens don't risk pathological backtracking.)
But I've used a rule. Like token patterns, rules also avoid the pathological backtracking risk. But, in addition rules interpret some whitespace in the pattern to be significant, in a natural manner. (See this SO answer for precise details.)
rules are typically appropriate towards the top of the parse tree. (Tokens are typically appropriate towards the leaves.)
rule TOP { <article>* }
The space at the end of the rule (between the * and pattern closing }) means the grammar will match any amount of whitespace at the end of the input.
<article> invokes another named rule in this grammar.
Because it looks like one should allow for any number of articles per bib file, I added a * (zero or more quantifier) at the end of <article>*.
rule article { '#article{' $<id>=<-[,]>+ ','
<kv-pairs>
'}'
}
If you compare this article pattern with the ones I wrote for the earlier Raku rules based solutions, you'll see various changes:
Rule in original one-liner
Rule in this grammar
Kept pattern as simple as possible.
Introduced <kv-pairs> and closing }
No attempt to echo layout of your input.
Visually echoes your input.
<[...]> is the Raku syntax for a character class, like[...] in traditional regex syntax. It's more powerful, but for now all you need to know is that the - in <-[,]> indicates negation, i.e. the same as the ^ in the [^,] syntax of ye olde regex. So <-[,]>+ attempts a match of one or more characters, none of which are ,.
$<id>=<-[,]>+ tells Raku to attempt to match the quantified "atom" on the right of the = (i.e. the <-[,]>+ bit) and store the results at the key <id> within the current match object. The latter will be hung from a branch of the parse tree; we'll get to precisely where later.
rule kv-pairs { <kv-pair>* % ',' }
This pattern illustrates one of several convenient Raku regex features. It declares you want to match zero or more kv-pairs separated by commas.
(In more detail, the % regex infix operator requires that matches of the quantified atom on its left are separated by the atom on its right.)
rule kv-pair { $<key>=\w* '={' ~ '}' $<value>=<-[}]>* }
The new bit here is '={' ~ '}'. This is another convenient regex feature. The regex Tilde operator parses a delimited structure (in this case one with a ={ opener and } closer) with the bit between the delimiters matching the quantified regex atom on the right of the closer. This confers several benefits but the main one is that error messages can be clearer.
I could have used the ~ approach in the /.../ regex in the one-liner, and vice-versa. But I wanted this grammar solution to continue the progression toward illustrating "better practice" idioms.
Constructing / deconstructing the parse tree
for $<article> { put "$<id>: $<kv-pairs><kv-pair>[0]<value>\n" }`
$<article>, $<id> etc. refer to named match objects that are stored somewhere in the "parse tree". But how did they get there? And exactly where is "there"?
Returning to the top of the grammar:
rule TOP {
If a .parse is successful, a single 'TOP' level match object is returned. (After a parse is complete the variable $/ is also bound to that top match object.) During parsing a tree will have been formed by hanging other match objects off this top match object, and then others hung off those, and so on.
Addition of match objects to a parse tree is done by adding either a single generated match object, or a list of them, to either a Positional (numbered) or Associative (named) capture of a "parent" match object. This process is explained below.
rule TOP { <article>* }
<article> invokes a match of the rule named article. An invocation of the rule <article> has two effects:
Raku tries to match the rule.
If it matches, Raku captures that match by generating a corresponding match object and adding it to the parse tree under the key <article> of the parent match object. (In this case the parent is the top match object.)
If the successfully matched pattern had been specified as just <article>, rather than as <article>*, then only one match would have been attempted, and only one value, a single match object, would have been generated and added under the key <article>.
But the pattern was <article>*, not merely <article>. So Raku attempts to match the article rule as many times as it can. If it matches at all, then a list of one or more match objects is stored as the value of the <article> key. (See my answer to "How do I access the captures within a match?" for a more detailed explanation.)
$<article> is short for $/<article>. It refers to the value stored under the <article> key of the current match object (which is stored in $/). In this case that value is a list of 3 match objects corresponding to the 3 articles in the input.
rule article { '#article{' $<id>=<-[,]>+ ','
Just as the top match object has several match objects hung off of it (the three captures of article matches that are stored under the top match object's <article> key), so too do each of those three article match objects have their own "child" match objects hanging off of them.
To see how that works, let's consider just the first of the three article match objects, the one corresponding to the text that starts "#article{garg2017patch,...". The article rule matches this article. As it's doing that matching, the $<id>=<-[,]>+ part tells Raku to store the match object corresponding to the id part of the article ("garg2017patch") under that article match object's <id> key.
Hopefully this is enough (quite possibly way too much!) and I can at last exhaustively (exhaustingly?) explain the last line of code, which, once again, was:
for $<article> -> $/ { put "$<id>: $<kv-pairs><kv-pair>[0]<value>\n" }`
At the level of the for, the variable $/ refers to the top of the parse tree generated by the parse that just completed. Thus $<article>, which is shorthand for $/<article>, refers to the list of three article match objects.
The for then iterates over that list, binding $/ within the lexical scope of the -> $/ { ... } block to each of those 3 article match objects in turn.
The $<id> bit is shorthand for $/<id>, which inside the block refers to the <id> key within the article match object that $/ has been bound to. In other words, $<id> inside the block is equivalent to $<article><id> outside the block.
The $<kv-pairs><kv-pair>[0]<value> follows the same scheme, albeit with more levels and a positional child (the [0]) in the midst of all the key (named/ associative) children.
(Note that there was no need for the article pattern to include a $<kv-pairs>=<kv-pairs> because Raku just presumes a pattern of the form <foo> should store its results under the key <foo>. If you wish to disable that, write a pattern with a non-alpha character as the first symbol. For example, use <.foo> if you want to have exactly the same matching effect as <foo> but just not store the matched input in the parse tree.)
Phew!
When the automatically generated parse tree isn't what you want
As if all the above were not enough, I need to mention one more thing.
The parse tree strongly reflects the tree structure of the grammar's rules calling one another from the top rule down to leaf rules. But the resulting structure is sometimes inconvenient.
Often one still wants a tree, but a simpler one, or perhaps some non-tree data structure.
The primary mechanism for generating exactly what you want from a parse, when the automatic results aren't suitable, is make. (This can be used in code blocks inside rules or factored out into Action classes that are separate from grammars.)
In turn, the primary use case for make is to generate a sparse tree of nodes hanging off the parse tree, such as an AST.
Footnotes
[1] Basic Raku is good for exploratory programming, spikes, one-offs, PoCs and other scenarios where the emphasis is on quickly producing working code that can be refactored later if need be.
[2] Raku's regexes/rules scale up to arbitrary parsing, as introduced in the latter half of this answer. This contrasts with past generations of regex which could not.[3]
[3] That said, ZA̡͊͠͝LGΌ ISͮ̂҉̯͈͕̹̘̱ TO͇̹̺ͅƝ̴ȳ̳ TH̘Ë͖́̉ ͠P̯͍̭O̚N̐Y̡ remains a great and relevant read. Not because Raku rules can't parse (X)HTML. In principle they can. But for a task as monumental as correctly handling full arbitrary in-the-wild XHTML I would strongly recommend you use an existing parser written expressly for that purpose. And this applies generally for existing formats; it's best not to reinvent the wheel. But the good news with Raku rules is that if you need to write a full parser, not just a bunch of regexes, you can do so, and it need not involve going insane!
I need to inject some code into an existing VB6 application.
What I would like to do is add logging code to the top of every method across a few hundred vb6 files, logging the method name and parameters with values.
The writing of the code is easy, but where I am struggling a bit is the matching of the method or property header in VB6 syntax, as there appears to be a great number of variations and optional keywords.
Has anyone got any suggestions about how to achieve this?
I have tried and failed with RegEx and have resorted to tokenising the code and looking for token patterns.
It may be easier to write it as a VB6 addin that allows you to enumerate all modules/procedures and insert code to suit.
Alternatively, use MZTools which is free and can add headers to individual procedures or new ones automatically.
You probably want something more robust then regular expressions for a project like this. I don't know of any OSS VB6 parser implementations off hand but I would recommend using a proper tool for this. This activity is sometimes called Aspect Oriented Programming or Mixins if you were to generalize the approach of injecting code at compile time.
I will take a moment to plug my own tool meta# which allows you to build a pattern matching grammar for exactly these types of scenarios but you could also use one of many others such as Lexx/Yacc, Flexx/Bison or ANTLR.
But even if you don't use mine specifically here is the general strategy I would take to solve the problem:
Create a code transformation (pre-compile) build step
Parse the files into an object model
Insert new objects into this model representing the logging calls
Generate new code files based on that object model
Compile the generated code only.
Generated code is a build artifact and is never edited or added to source control.
Run this transform step whenever you build.
Our DMS Software Reengineering Toolkit with its Visual Basic front end could be used to do this.
DMS parses source text using a front end to abstract syntax trees, and then enables arbitrary analysis/transformation to be applied to those trees. Many transformation changes can be accomplished using source-to-source program transformation, in which code is rewritten using "if you see this syntax, replace it by that syntax", using the grammar as a way to define abstract placeholders. This makes it relatively easy to write transformations on code using familiar syntax. This generalizes OP's method of trying to match sequences of tokens.
The OP's problem could be posed as aspect like rewrites of the form:
default domain VisualBasic~VB6;
rule function_insert_log_call(a: attributes, t: type,
i: IDENTIFIER, p: parameters, s:statements)
= function -> function
= " \a FUNCTION \i ( \p ) AS \t
\s
END FUNCTION"
-> "\a FUNCTION \i ( \p ) AS \t
my_log(\tostring\(\i\))
\s
END FUNCTION";
rule subroutine_insert_log_call(a: attributes,
i: IDENTIFIER, p: parameters, s:statements)
= subroutine -> subroutine
= " \a SUB \i ( \p )
\s
END SUB"
-> " \a SUB \i ( \p )
my_log(\tostring\(\i\))
\s
END SUB";
These rewrites are of the form
rule *rulename* ( *patternvars* ) *nonterminal* -> *nonterminal*
= " *syntaxpattern* "
-> " *syntaxpattern* ";
The specific rules provided will recognize the function headers and bodies regardless of content/whitespace/comments because they actually match against the ASTs.
The "..." are metaquotes, and what is outside is DMS rule syntax, and inside
is VB6 syntax. The \n inside the "..." represents an (AST)
parameter that must match a grammar nonterminal N declared in the rule
header as ...n:N.... tostring is a custom meta-function (called with meta parens ( ) )
that converts a tree node argument into a tree node for a literal string.
OP might need more rules than that to handle other cases; perhaps he wants logging
of GOSUB calls, and/or to capture function parameters in the log call.
Other answer suggest getting a parser generator and, well, defining VB6 to enable parsing. It is important to understand that getting the VB6 syntax right is really hard; the langauge is poorly documented and and has some really wierd rules about whitespace, statements-within-lines and statements across line boundaries. If you don't get this right, you simply can't parse hundreds of files. We had to define our own grammar (as we have for DMS for
many other languages).
You can read more about code instrumentation/logging using program transformations
here
I have what I imagine will be a fairly involved technical challenge: I want to be able to reliably alpha-rename identifiers in multiple languages (as many as possible). This will require special consideration for each language, and I'm asking for advice for how to minimize the amount of work I need to do by sharing code. Something like a unified parsing or abstract syntax framework that already has support for many languages would be great.
For example, here is some python code:
def foo(x):
def bar(y):
return x+y
return bar
An alpha renaming of x to y changes the x to a y and preserves semantics. So it would become:
def foo(y):
def bar(y1):
return y+y1
return bar
See how we needed to rename y to y1 in order to keep from breaking the code? That is why this is a hard problem. It seems like the program would have to have a pretty good knowledge of what constitutes a scope, rather than just doing, say, a string search and replace.
I would also like to preserve as much of the formatting as possible: comments, spacing, indentation. But that is not 100% necessary, it would just be nice.
Any tips?
To do this safely, you need to be able to to determine
all the identifiers (and those things that are not, e.g., the middle of a comment) in your code
the scopes of validity for each identifer
the ability to substitute a new identifier for an old one in the text
the ability to determine if renaming an identifier causes another name to be shadowed
To determine identifiers accurately, you need a least a langauge-accurate lexer. Identifiers in PHP look different than the do in COBOL.
To determine scopes of validity, you have to be determine program structure in practice, since most "scopes" are defined by such structure. This means you need a langauge-accurate parser; scopes in PHP are different than scopes in COBOL.
To determine which names are valid in which scopes, you need to know the language scoping rules. Your language may insist that the identifier X will refer to different Xes depending on the context in which X is found (consider object constructors named X with different arguments). Now you need to be able to traverse the scope structures according to the naming rules. Single inheritance, multiple inheritance, overloading, default types all will pretty much require you to build a model of the scopes for the programs, insert the identifiers and corresponding types into each scope, and then climb from the point of encounter of an identifier in the program text through the various scopes according to the language semantics. You will need symbol tables, inheritance linkages, ASTs, and the ability to navigage all of these. These structures are different from PHP and COBOL, but they share lots of common ideas so you likely need a library with the common concept support.
To rename an identifier, you have to modify the text. In a million lines of code, you need to point carefully. Modifying an AST node is one way to point carefully. Actually, you need to modify all the identifiers that correspond to the one being renamed; you have to climb over the tree to find them all, or record in the AST where all the references exist so they can be found easily. After modifyingy the tree you have to regenerate the source text after modifying the AST. That's a lot of machinery; see my SO answer on how to prettyprint ASTs preseriving all of the stuff you reasonably suggest should be preserved.
(Your other choice is to keep track in the AST of where the text for the string is,
and the read/patch/write the file.)
Before you update the file, you need to check that you haven't shadowed something. Consider this code:
{ local x;
x=1;
{local y;
y=2;
{local z;
z=y
print(x);
}
}
}
We agree this code prints "1". Now we decide to rename y to x.
We've broken the scoping, and now the print statement which referred
conceptually to the outer x refers to an x captured by the renamed y. The code now prints "2", so our rename broke it. This means that one must check all the other identifiers in scopes in which the renamed variable might be found, to see if the new name "captures" some name we weren't expecting. (This would be legal if the print statement printed z).
This is a lot of machinery.
Yes, there is a framework that has almost all of this as well as a number of robust language front ends. See our DMS Software Reengineering Toolkit. It has parsers producing ASTs, prettyprinters to produce text back from ASTs, generic symbol table management machinery (including support for multiple inheritance), AST visiting/modification machinery. Ithas prettyprinting machinery to turn ASTs back into text. It has front ends for C, C++, COBOL and Java that implement name and type resolution (e.g. instanting symbol table scopes and identifier to symbol table entry mappings); it has front ends for many other langauges that don't have scoping implemented yet.
We've just finished an exercise in implementing "rename" for Java. (All the above issues of course appeared). We about about to start one for C++.
You could try to create Xtext based implementations for the involved languages. The Xtext framework provides reliable infrastructure for cross language rename refactoring. However, you'll have to provide a grammar a at least a "good enough" scope resolution for each language.
Languages mostly guarantee tokens will be unique, whatever the context. A naive first approach (and this will break many, many pieces of code) would be:
cp file file.orig
sed -i 's/\b(newTokenName)\b/TEMPTOKEN/g' file
sed -i 's/\b(oldTokenName)\b/newTokenName/g' file
With GNU sed, this will break on PHP. Rewriting \b to a general token match, like ([^a-zA-Z~$-_][^a-zA-Z0-9~$-_]) would work on most C, Java, PHP, and Python, but not Perl (need to add # and % to the token characters. Beyond that, it would require a plugin architecture that works for any language you wanted to add. At some point, there will be two languages whose variable and function naming rules will be incompatible, and at that point, you'll need to do more and more in the plugin.