Plisp: Lisp/S-expression parser library
Plisp is a C library for parsing Lisp/S-expressions. I wrote it because I got massively sick of writing the same code every time I wanted to parse a text file.
I'd like some testers/users for this. It suits *my* needs, but I'm not too good at accommodating other people's. Do give it a try.
Installation:
I decided to mix it up and use Mercurial instead of Git. I'm liking the change.
AUR package is here: http://aur.archlinux.org/packages.php?ID=35422
hg clone URI (also web view): http://peasantoid.org:1024/plisp
Manual installation:
$ root=/path/to/root_directory ./make install
Documentation:
Sorely lacking. I will attempt to write some of this later; in the meantime, look at the source (particularly header files) and everything in test/.
Technical details:
Text is processed in two stages. The first, tokenization, iterates through the text looking for 'simple' tokens (left/right parentheses, quotes, numbers, strings, symbols, etc.). The second, parsing, iterates through the token list and converts it to a parse tree.
POSIX ERE (extended regular expressions) are used for tokenization. Seriously, this is really handy. $(man 3 regex) for details.
Linked lists are heavily relied upon.
Note that numbers are just stored as strings. It's up to the programmer to change those to actual numbers (f.e. strtol(), strtod()).
Testing:
The distribution includes a simple syntax-dumper utility that takes data from stdin, parses it, and formats the resulting syntax tree to stdout. My terminal transcript follows:
narch plisp -> ./make test && build/test/dump
---[RUN test (lib)]
---[RUN lib (obj)]
---[RUN obj ()]
build/obj/error.o
build/obj/escape.o
build/obj/init.o
build/obj/list.o
build/obj/parser.o
build/obj/tokenizer.o
---[END obj]
build/libplisp.so
build/libplisp.a
build/include/*.h
---[END lib]
build/test/dump
---[END test]
(foo '("bar") `(3.456 ,(baz 4 5)))
^D
1:1 list: ...
1:2 symbol: foo
1:7 list (quoting: '): ...
1:8 string: bar
1:16 list (quoting: `): ...
1:17 real: 3.456
1:20 list (quoting: ,): ...
1:21 symbol: baz
1:25 integer: 4
1:27 integer: 5
Tested by/on:
me: Arch 64-bit (x86_64 Intel Core 2 Duo (Apple MacBook3,1))
me: Arch 64-bit (x86_64 Intel Xeon (Xen))
me: ArchPPC (32-bit PowerPC processor (Apple Mac Mini G4))
If you test this, please post your architecture and processor type. I really hate those insidious system-specific bugs.
Last edited by Peasantoid (2010-03-13 05:31:46)
Peasantoid wrote:Interesting thing I discovered: you have to pass '-lm' to GCC in order to get it to link with the math functions. Does anyone know why this isn't in libc?
I've encountered this before, it's one of those things that make you go "huh?". Nice work on getting the math module done
As a suggestion, it would be useful to have a module which allows loading and running arbitrary functions from shared libraries, although I'm not too sure where to start with implementing this, I think there is a library around that allows you to do this fairly easily, but I can't seem to find it right now. But as a relatively new scripting language something like this would make it easier to interact to common libraries while other modules are still being written.
Edit: Obviously I was searching for the wrong thing, what I'm talking about is a foreign function interface
Last edited by HashBox (2009-06-13 01:43:44)
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Template Expressions in Library Items?
Hi All,
The quick question is this: can template expressions be made
to work inside library items?
Here’s the situation…
The page:
http://www.fretbank.com/basics/intervals/index.html
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here's the code if it helps:> Is having the link outside the div a problem in older
browsers?
It's invalid HTML. That's enough for me. And I suspect it
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problem somewhere, as you are trying to make the entire
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> This allows me to only have to change each of these nav.
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I would opt for a single template structured so that changes
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server-side
includes for the navigation elements, and place them into
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Murray --- ICQ 71997575
Adobe Community Expert
(If you *MUST* email me, don't LAUGH when you do so!)
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"Fret Man" <[email protected]> wrote in
message
news:[email protected]...
> Thanks for the reply Murray.
>
> A couple clarifications and questions. Sorry for the
length, but I felt it
> was
> better to be clear than concise.
>
> I am using nested templates.
>
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> find a
> balance between flexibility and work load.
>
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>
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>
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>
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Regard,
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... and one missed opportunity to learn something
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Regular expression - parse version number string
Hi,
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Best Regards,
Michaelheissm wrote:
Hi,
I try to parse a string using regular expressions but id did not work correctly in all cases.
The string that i want to parse can have one of the following layout:
3.4.5.v20090305 or
3.4.5The first three parts have to be integer values, the last part can be a free string (which is optional).
I use the following code to parse the version number and extract the parts:
Pattern versionPattern = Pattern.compile("(\\d+)\\.{1}(\\d+)\\.{1}(\\d+)(?:\\.{1}(\\w+))?");
Matcher m = versionPattern.matcher(versionString);
if (!m.find()) {
throw new IllegalArgumentException("Version must be in form <major>.<minor>.<micro>.<qualifier>");
// assert that we matched every part
// three groups (without qualifier) or four parts (with qualifier)
int groups = m.groupCount();
if (groups != 4) {
throw new IllegalArgumentException("Version must be in form <major>.<minor>.<micro>.<qualifier>");
// extract the parts
major = parseInt(m.group(1));
minor = parseInt(m.group(2));
micro = parseInt(m.group(3));
qualifier = m.group(4);The above regular expression works in all cases that i tested, except one.
The follwoing string is accepted as correct input: (but it shouldn't)
3.4.5a.v20090305And i get the result:
major = 3
minor = 4
micro = 5
qualifier = a.v20090305No, that can't be the output. Perhaps you have some old class files you're executing, because with the code you now posted, that can't be the result.
To verify this, execute this:
import java.util.regex.*;
public class Main {
public static void main(String[] args) {
String versionString = "3.4.5a.v20090305";
Pattern versionPattern = Pattern.compile("(\\d+)\\.{1}(\\d+)\\.{1}(\\d+)(?:\\.{1}(\\w+))?");
Matcher m = versionPattern.matcher(versionString);
if (!m.find()) {
throw new IllegalArgumentException("Version must be in form <major>.<minor>.<micro>.<qualifier>");
// assert that we matched every part
// three groups (without qualifier) or four parts (with qualifier)
int groups = m.groupCount();
if (groups != 4) {
throw new IllegalArgumentException("Version must be in form <major>.<minor>.<micro>.<qualifier>");
// extract the parts
System.out.println("1 -> "+m.group(1));
System.out.println("2 -> "+m.group(2));
System.out.println("3 -> "+m.group(3));
System.out.println("4 -> "+m.group(4));
}and you'll see that the following is the result:
1 -> 3
2 -> 4
3 -> 5
4 -> nullSome remarks about your pattern:
"(\\d+)\\.{1}(\\d+)\\.{1}(\\d+)(?:\\.{1}(\\w+))?"All the "{1}" can be omitted they don't add anything to your regex and are only cluttering it up. And you'll probably also want to "anchor" your regex using the start- and end-of-string-meta-characters, like this:
"^(\\d+)\\.(\\d+)\\.(\\d+)(?:\\.(\\w+))?$" -
Expression parsing and execution
Hi All,
I need ideas/code/suggestions from you all. I am working on a Formula Builder UI. In this a user can create their own expressions choosing some variable values also.
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I am trying to evaluate an expression like this =IF(A1<0.125,0.0005,(IF(A1<0.25,0.00066667,(IF(A1<0.5,0.00075,(IF(A1<0.75,0.000916667,0.0010833))))))) in java. In excel it is easy but i cannot use that. I cannot use any free downloads. Is there any code sample which I can use to start off? I need to parse and evaluate the above expression. -
Command line arguments C++ parsing library [SOLVED]
Hi,
i'm looking for such a library. Requrements:
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Regular Expression - Parse CSV
"Q-Accept, Other Employment"
I need to remove the "," from the above string. The CSV File
I have includes commas inside quotetaion marks, I need to remove
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AndyI think the previous poster may have a typo in the example
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Try changing this...
<cfset modifiedString = ReReplace(string, '["]', '',
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/>
Good luck! -
Parsing an Algebraic Expression
Hi ,
Can any body provide me an idea to parse an algebraic expression in Java.Are there any built in classes for parsing an expression and evaluating after substituting the values for variables in the expression?
If no classes are availble,plz provide me any algorithm for doing that.
Thanks in AdvanceObserve:
Parsing an expression is essentially the act of converting the expression from infix notation to postfix notation. Infix requires parens and precedence to specify order of operations but post fix unambiguously specifies them by the order of the tokens
So something like
"a+b*c" becomes "a b c * +"
"a*b+c" becomes "a b * c +"
"(a+b)*c" becomes "a b + c *"
notice that arguments (variables and numbers, the leaves of the implied expression tree) occur in the same sequence in both the infix and the postfix notation. Thus you can view the parsing as a filtering process that passes arguments directly from input to output and all the filter is doing is re-arranging the order of the operators.
All this rearranging of operators can be done with a single stack and it is all based on this observation:
When you saw a string like "a op1 b op2 c" you run across the token for the first operator before you have even collected its right argument. You must put that operator somewhere and a OpStack is the place to put it. You don't know whether to emit op1 until you have had a look at the next operator, op2. If op2 was higher priority than op1, then op2 gets to consume the argument b first. In that case op2 just gets added to the stack on top of op1.
However if op2 was less than or equal in precedence to op1, well then op1 can now be flowed to the output stream and allowed to act on the b argument that is already out on the output stream.
This means that the fundamental operation of the expression parser is the business of pushing an opertor token onto the stack, but first spewing to the output all the other operators on the stack that had a higher or equal priority. If we give this function a name like opStack.pushSpew(token) it could look something like this:
class OpStack{
Stack s = new Stack();
void pushSpew(List out, Token t){
Token tos;
while(!s.empty() && (tos = peek()).priority >= t.priority){out.add(pop());}
push(t);
}Next thing to observe is that a grouper, like open and close parens, behaves in the following way. An open paren acts like a very high priority operator when pushed to the stack in that it spews nothing. The previous op is NOT allowed to eat the argument that is about to come right after the open paren. However once the open paren marks the stack, the open should be a lower priority than any real op that gets pushed onto the stack above it because it must delay going out until every real op in the group had its shot. The close paren should also act like a very low priority op. It should spew every op upto but not including the open paren that started this group.
As a computation trick, if you set the priority of an open lowest of all, and the priority of a close just above that, and you just push the open onto the stack instead of pushSpewing it onto the stack, you will get the desired behavior. You with then pushSpew the close paren and it will dump everything from the stack to the output up to but not including the open. At this point it is easy to check the balance. If you do not have an open/close pair sitting as the top two elements on the stack then the parens (or the brackets or the braces) were not properly nested.
We are almost done. There are post fix operators like factorial and prefix operators like minus that we need to deal with. It only makes sense to evaluate these suckers from the inside out i.e. if you had a string of prefixs on an arg
op1 op2 op3 arg
the only sensible order is defined by parens like this
(op1 (op2 (op3 arg) ) )
and in post fix that would be
arg op3 op2 op1
that is exactly what you would get if you just pushed each prefix op onto the stack in the order you saw them and then popped them off after you dumped out the argument.
Post ops should also work from the inside out
arg op1 op2
being
( (arg op1) op2 )
and you get this behavior by just dumping a post op to the output when you see it.
There is only one special concern. What should you do if you saw, both pre ops and post ops on the same arg?
is "op1 arg op2" done like this: "(op1 arg) op2" or "op1 (arg op2)"? Well, why should these be any different from regular diadic ops, let precdence decide. An espression like minus three factorial "-3!" should be interpreted as take the factorial of 3 and then negate it (and not the other way around!) so let the priority of factorial be greater than that of minus and just do the standard pushSpew with post ops to let them spew out any high priority pre ops before they go onto the stack, but then unlike binary ops, the post op immediately comes off the stack and goes to the output because post ops bind up right away.
Now if you are not careful with your precedences you could get "wierd" behavior. If for example you did not assign a high priority to a factorial, you could write expressions like "3+4!" and the priority would treat that like "(3+4)!" the plus would bind tighter than the factorial. It is hard for me to imagine a language where you would want the effects of either a postfix or a prefix operator to span across multiple arguments combined by single diadic operator, but that is really up to you. You certainly could have a language where you gave a very low precedence to ~ which could mean the boolean NOT, a lower precedence than the diadic operator >= which would allow you to write "~ a >= b" which would mean "~(a>=b)"
After all it is your language, do what you want. None the less I would advise against alowing ANY pre or post op to have a priority LESS than that of ANY diadic operator.
Lots of talk here but to recap, the code is quite simple:
while((t = getNextToken()) != null){
switch (t.type()){
case ARG: out.add(t); break; // arguments pass straight to output
case PRE: stack.push(t); break; // pre ops are just pushed (binding them to the next arg)
case OPEN: stack.push(t); break; // Opens just push, they don't spew to output
case DI: stack.pushSpew(out,t); break; // Diadic ops do the standard pushSpew
case POST: stack.pushSpew(out,t); out.add(stack.pop()); break; //spew and then go out
case CLOSE: stack.pushSpew(out,t); stack.removeOCpair(); // spew all ops in group
// and then check if you had a balancing open
}That just about does the entire parse. If you can find the tokens in the input you can rearrange them into the output. You do need to flush the opStack when you are done with the input stream and there is a convenient trick to doing that. The trick is this. Invent an invisible Open and Close pair, invisible meaning that they never show up in any input stream, you just made them up and pretended that that expression started with an invisible OpenExp and at the end it closed with a CloseExp.
The CloseExp at the end will act like any grouper, it will flush the stack looking for the corresponding opener. IF there was any unbalanced grouper, like say an extra unbalanced open paren somewhere in the expression, the CloseExp will spew its way down to that unbalanced paren and then fail when it discovers that it does not match the open in the call to remove the OC pair. The is a way to do error detection. Use a fictional group on the entire expression to both flush the remainder of the opStack and to do a final check for unbalanced groupers.
In fact, while we are on the topic of error checking there is another one that is very good to include. Basically in a real expression if you ignore the parens, the progression should be an alternation between args and diadic ops, with an occasional pre or post op thrown in.
A simple count tells you where you are. Go up to 1 when you pass an argument, go back down to zero when you see a diadic operator. You should start at zero, because there have been no arguments or ops yet. In state zero the only legal things to do are to put in a pre op or an arg. Once you have an arg out there the only legal things to do are to have a post op or a diadic op. This little state machine will tell you if and when you have got either a pair of arguments together with no op between them, or a pair of ops with no argument between them. You should start at state = 0 and you should end at state = 1 (unless you allow empty expressions) So we can beef up the error checking with a very simple addition. The guts of the parse will now look like this:
state = 0
stack.push(Token.OpenExp); // start off with an open of the expression
while((t = getNextToken()) != null){
switch (t.type()){
case ARG: assertStateIs(0); out.add(t); state = 1; break;
case PRE: assertStateIs(0); stack.push(t); break;
case OPEN: stack.push(t); break;
case DI: assertStateIs(1); stack.pushSpew(out,t); state =0; break;
case POST: assertStateIs(1);stack.pushSpew(out,t); out.add(stack.pop()); break;
case CLOSE: stack.pushSpew(out,t); stack.removeOCpair();
stack.pushSpew(out,Token.CloseExp); stack.removeOCpair();
assertState(1);
return out;So - there it is, in outline form the way that you parse an expression.You build 3 classes, Token, ExpressionParser, and OpStack
Token is just a bucket that holds a name, a type (ARG, PRE, OPEN, DI, ...) and a precedence.
OpStack is just a wrapper for a reqular stack that will hold Tokens and allow for a pushSpew function.
ExpressionParser is little other than a Map full of all your Tokens. This map allows the parser to map substrings, tokens, that it finds in the input like >= to actual Tokens with a capital T. It will have two main methods:
1) the parse method which I have almost completly written for you. It takes an input string and will fill up an output list placing the Tokens in post fix order, which is your parse tree.
2) the routine getNextToken which will walk the input string, skipping white space when appropriate, looking for names, numbers, and operators and building each chunk that it finds into a Token.
One last complexity note. If you want to allow functional notation like sqrt(3) you are using parens in a fundamentally different way than was described above (ditto when you use brackets to represent array indexing like x[5]) the fundamentally different thing that you are doing is that you are allowing an argument (a name) like "sqrt" to sit right next to another argument like "3" with no binary op in between. You are using an "implied" binary op at that point. You have saved the user from typing "sqrt FUNCTIONCALL (3)" or "x ARRAYINDEX 5"
I will leave it as an exercise to the reader to see how you make a small modification to the OPEN case to detect and deal with an implied operation. Don't forget that you must tell the state error checker what you are doing.
And now that I have shown you how fundamentally simple it is to build an expression parser let me comment on why you do not find a standard library routine for doing this.
The primary reason is that there is no such thing as a "standard" math expression. Parsing is based on a language and there is no one language. Are you going to allow hex numbers in your expressions? How about scientific notation? Is = equality or assignment? Do you allow functional notation? Array indexing? Multi-dimensional array (like x[2,3])? How about string constants like "foobar"? How do you embed quotes in your quoted strings? Are you allowing comments, block comments, statements, code, Lisp expressions, complex numbers, implicit type conversion, type casting? At what point does it stop being a simple expression and start being a full computer language?
Furthermore, most of the work you will quickly see if you use what I have suggested to build an expression parser, it how to give your user feedback that the expression that he typed had problems and where. There is no stardard UI for error feedback in things that don't parse correctly. Are you just going to dump cryptic strings to the console or are you going to highlight something in a text box somewhere?
All the work turns out to be that of defining your language and determining your set of tokens and what precedence you will employ. Once you get that all worked out, parsing the expressions only takes the ten or fifteen lines of code that I outlined.
And look, it only took several thousands of words to explain why it only takes about 15 lines of code to parse expressions once you have decided upon your language and written your tokenizer.
Enjoy -
Binary tree for parsing algebraic expressions
hi all
i have a project to do.. i need to read in an algebraic expression, parse it and form a binary tree. later use that tree to evaluate the expressions when the actual value for those variables are passed..
can anyone tell me how to go about doing this.
im a beginner in java..
tksfirst of, your going to need three stacks. The implementation of a stack in JAVA is something that's easy to find, do a forum search. Your going to need a Binary Node as well. One stack will hold the operator elements of your algebraic expression, another will hold the numeric values, and the final will hold your binary nodes:
expression: 4 + 6 - (6 * 9)
now there are some rules that should be followed. Whenever a closing parenthesis is encountered ")", pop an operator, pop two numbers, and create the corresponding binary node.
order of operations:
push 4 onto numberStack
push + onto operatorStack
push 6 onto numberStack
push - onto operatorStack
push ( onto operator Stack
push 6 onto numberStack
push * onto operatorStack
push 9 onto numberStack
")" encountered
Now, your stacks look something like this:
operatorStack: [ +, -, (, *, ) ]
numberStack: [ 4, 6, 6, 9 ]
pop 9 and 6 from numberStack, pop * from operatorStack
build a binaryNode using these three elements
push this node onto the binaryNodeStack
I.E. using the expression above:
/ \ is the resulting binary node once the ")" is received.
6 9
etc.. there are some rules regarding when to pop and build binary nodes, it's been a while since i did this assignment and frankly my brain hurts, hope this gets you started, good luck. -
NEED HELP:To Parse Conditional Operator Within An Expression.
Hi there:
I'm having some difficulties to parse some conditoional operator. My requirements is:
Constants value: int a=1,b=2,c=3
Input/Given value: 2
conditional operator expression: d=a|b|c
Expected result: d=true
Summary: I like to receive a boolean from anys expressions defined, which check against Input/Given value.Note: The expression are various from time to time, based on user's setup, the method is smart enough to return boolean based on any expression.
Let me know if you have any concerns.
Thanks a million,
selenahere is a simple example.
BNF changes
EXPR ::= OPERATOR
EXPR ::= OPERATION OPERANT EXPR
This is as far as I can go, please use it as a template only
because you need to take into account the precedence using ()
the logic of the eval was simply right to left so I think it is not what you want
Cheers
public interface Expression
String OR = "|";
String AND = "&";
public boolean eval(int value) throws Exception;
public class ExpressionImpl implements Expression
public String oper1;
public String operant;
public Expression tail;
/* (non-Javadoc)
* @see parser.Expression#eval()
public boolean eval(int value) throws Exception
int val1 = getValue(oper1);
if (null == tail)
System.out.println(val1 + ":" + value);
return (val1 == value);
else
if (OR.equals(operant))
return (val1 == value || tail.eval(value));
else if (AND.equals(operant))
return (val1 == value && tail.eval(value));
else
throw new Exception("unsupported operant " + operant);
private int getValue(String operator) throws Exception
Integer temp = ((Integer)Parser.symbol_table.get(operator));
if (null == temp)
throw new Exception("symbol not found " + operator);
return temp.intValue();
public String toString()
if (null == operant) return oper1;
return oper1 + operant + tail.toString();
public class Parser
public static HashMap symbol_table = new HashMap();
* recursive parsing
public Expression parse(String s)
ExpressionImpl e = new ExpressionImpl();
e.oper1 = String.valueOf(s.charAt(0));
if (s.length() == 1)
return e;
else if (s.length() > 2)
e.operant = String.valueOf(s.charAt(1));
e.tail = parse(s.substring(2));
else
throw new IllegalArgumentException("invalid input " + s);
return e;
public static void main(String[] args) throws Exception
Parser p = new Parser();
Parser.symbol_table.put("a", new Integer(1));
Parser.symbol_table.put("b", new Integer(2));
Parser.symbol_table.put("c", new Integer(3));
Parser.symbol_table.put("d", new Integer(4));
Expression e = p.parse("a|b|c&d");
System.out.println("input " + e.toString());
System.out.println(e.eval(2));
} -
Simulating a program like Outlook express for a Online Store
Hi all,
I want to create a program that should read all the information come to me on a website using my user name and password. Some times i need to edit or add information on the site. The website will have sessions and cookies enabled. I don't know how to do it. Any help in any application is greatly appreciated.
I have a new project assigned to me. That is for my inhouse needs, I need to update the data in a site . This site will give a username and password to all the members. We are one of the members. But we have to simulate a tool to update the products in their site.
It will be something like outlook express but not a mailing interface.
Let me explain outlook first. Out look is getting the username and password from the user and then logs in into the users account in the website (yahoo or hotmail anything). And then they are going to the mail section and taking the mails if there were any. Same thing for composing a mail.
But I am not considered with mails. Here the data is like product information. They may already be there, or they may be new items. I will have to keep a local database here and to synchronize this database with the website.Hi again.
Well, your headed for a lot of trouble. I sugest you try to find and HTTP library and and HTML parsing library.
If HTTP library should allow you to make the request and the HTML parsing to save the trouble of writing a parser. But you will need to know wher to find in the parsed structure the data you need. This is the problem.
The Swing package contains an HTML parsing system: check the package javax.swing.text.html adn javax.swing.text.html.parser. Maybe these will do for the parsing and the Gets, the post I don't know...
The experience I have with this was in building a small web server, not a client :-)
Hope this helps,
Nuno -
SSRS Dataset Filter expression query
I have an SSRS report which has a simple dataset and accepts two date parameters, and filters the results based on a Position parameter. The Position parameter filter is:
Expression: Position
Operator: In
Value: [@Position]
I have now been told that each position has a few other aliases in the database against the Position column. i.e. For a Position of "Contractor" I now also need to return "Consultant" records, based on the same field. Note, only one Position
can be selected at a time.
I imagine I have to update the Value expression above to do something like:
- When @Position in "Contractor" also return rows where Position is x, y, z (I am happy to hard code these)
I have about 10 Positions each with one or more aliases - can someone help guide me on how to set up the expression?
Thanks!Thanks Ione.
Ok - I have set my parameter values in the value box, comma separated
My dataset filter for the param Operator is set to IN and the value [@Position]
However where I have multiple values set against a position I do not get any results (there is data in the DB)
Do I need to do something different when setting the paramter values? i.e. use the expression and then a function to parse the comman separted values
Or - something in the Filter to make the expression parse the incoming paramter?
Thanks again
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