I need to use writeln specifically in Prolog with a variable in it. What I am trying to make is an error that takes the first element of a list, and format does what I need almost perfectly, but again it specifically needs to be writeln.
I experimented for awhile and tried using '+' to concatenate the string like how it works in other languages, and when I use this
writeln("ERROR: \"" + Head + "\" is invalid.")
I almost succeed in what I want, and it prints
ERROR: " + a + " is invalid.
with the variable 'a' highlighted (another requirement) when I am trying to get
ERROR: "a" is invalid.
But I am unable to print it without using characters such as +, -, or | to contain the variable. I don't really understand what is going on and I haven't been able to find a reason on my own.
Using string_concat twice makes the proper string, but the variable is not highlighted like it is supposed to be.
As you already mentioned, using string_concat solves your problem as you want. String concatenation does not work like this in Prolog as it does in different languages. The reason why it still prints something when using the + while it throws without it is that the + is in an infix operator and is displayed as such in when using writeln because it also writes out the predicate names.
It will write the + infix when provided as prefix such as in this example:
writeln(+(3,2)).
It does not work without the + because then you simply have three different values after another. Quoted Atom, Variable filled with an Atom, Quoted Atom. Prolog expects a term though, so you run into a syntax error.
Related
In a situation like this for example:
[% $create_port %]
or [list [% $RTL_LIST %]]
I realized it had to do with the brackets, but what confuses me is that sometimes it is used with the brackets and variable followed, and sometimes you have brackets with variables inside without the %.
So i'm not sure what it is used for.
Any help is appreciated.
% is not a metacharacter in the Tcl language core, but it still has a few meanings in Tcl. In particular, it's the modulus operator in expr and a substitution field specifier in format, scan, clock format and clock scan. (It's also the default prompt character, and I have a trivial pass-through % command in my ~/.tclshrc to make cut-n-pasting code easier, but nobody else in the world needs to follow my lead there!)
But the code you have written does not appear to be any of those (because it would be a syntax error in all of the commands I've mentioned). It looks like it is some sort of directive processing scheme (with the special sequences being [% and %], with the brackets) though not one I recognise such as doctools or rivet. Because a program that embeds a Tcl interpreter could do an arbitrary transformation to scripts before executing them, it's extremely difficult to guess what it might really be.
I would like to implement a small subset of siri/cortana like features in command line.
For e.g.
$ What is the sum of 100 and 1000
> Response: 1100
$ What is the product of 10 and 12
> Response: 120
The questions are predefined regular expressions. It needs to call the matching function in ruby.
Pattern: What is the sum of (\d)+ and (\d)+
Ruby method to call: sum(a,b)
Any pointers/suggestion is appreciated.
That sounds exactly like cucumber, maybe take a look and see if you can just use their classes to hack something together :) ?
You could do something like the following:
question = gets.chomp
/\A.*(sum |product |quotient |difference )\D+([0-9]+)\D+([0-9]+).*\z/.match question
send($1, $2.to_i, $3.to_i)
Quick explanation for anyone that may be new to matching in Ruby:
This gets a line of input from the command line and scans it for a function name (i.e. sum, product, etc) followed by a space and potentially some non-digit characters. Then, it looks for a first number (similarly followed by a space and 0 or more non-digit characters) and a second number followed by nothing or anything. The parentheses determine what gets assigned to the variables preceded by a $, i.e. the substring that matches the contents of the first set of parentheses gets assigned to $1.
Next, it calls the method whose name is the value of $1 with the arguments (casted to integers) found in $2 and $3.
Obviously, this isn't generalized at all--you're putting the method names in the regex, and it's taking a fixed number of arguments--but it'll hopefully be useful for getting you on the right track.
I have read this entry (http://stackoverflow.com/questions/8513185/vbscript-to-correctly-re-format-a-delimited-text-file) many times and still do not understand the .Execute section.
WScript.Echo oTDb.Execute(Replace("SELECT * FROM [#T]", "#T", sTbl1)) _
.GetString( adClipString, , "|", vbCrLf, "" )
The pieces I am having trouble with are the [#T] and "#T".
I know it is the "#T" that is reading the filename in the schema file and and the [#T] must be using the "#T" as a substitute. What I cannot find out is where this is mentioned/spoken about.
Some addition questions I have are:
1. If the filename can be substituted with a variable then what else can?
2. What are the rules for maintaining variables
Do they have to start with the # symbol
Are there any reserved words
If they have to start with the # symbol, does the next character have to be a letter
As I am responsible for #Milton's worry/puzzlement:
There is no variable interpolation/substitution in VBScript. Other languages - e.g. Perl - will splice variables or even expression results into string literals when you mark the replacements with special symbols. No such funny letters in VBScript.
SQL dialects allow parameterized commands in which parts to be replaced are marked by ? and/or names prefixed by symbols like #. But here ADO never sees the #T - VBScript's Replace() function has interpolated the table name before the resulting strings is send to .Execute().
Building complex strings from parts (SQL statements, commandlines for .Run or .Exec, ...) by concatenation is cumbersome. The most important drawback is that you can't (proof) read the string anymore for all those " and &.
A simple workaround is to use Replace(), as in
[sResult = ] Replace("SELECT * FROM [#T]", "#T", sTbl1)
I used the # just for letting the placeholder stand out. As you would have to stack/nest the Replace() calls when you need more substitutions on the template, other strategies are worth considering:
writing a function that takes a template string and a dictionary of replacements to apply Regexp.Replace() to the string
using .NET's System.Text.StringBuilder and its .AppendFormat to do the slicing in a sprintf like style
I am trying to display a network share path in my Prolog output code.
The path is like :
\\fileserver\path\to\file.txt (ex1)
or
\\\\fileserver\\path\\to\\file.txt (ex2)
but If I try displaying it using format :
pri(Z):-
format('Printing Zx : \"~w\"',[Z]).
the slashes get truncated to
\fileserverpathtofile.txt (ex1)
Obviously some times, the path may contain \\\\ in which case the display is correct.
How to make it print proper path?
Any help please.
Thanks.
In the Prolog atoms backslash is a meta-character, i.e. if you want your atom to contain a backslash character then you need to escape it using the backslash character. E.g. in order to represent the Windows path \\fileserver\path\to\file.txt as a Prolog atom you need to write
Path = '\\\\fileserver\\path\\to\\file.txt'.
In principle there are two ways of printing stuff out, one for the humans (pretty-printing), using write
?- Path = '\\\\fileserver\\path\\to\\file.txt', write(Path).
\\fileserver\path\to\file.txt
and one for the machines (serializing), using write_canonical
?- Path = '\\\\fileserver\\path\\to\\file.txt', write_canonical(Path).
'\\\\fileserver\\path\\to\\file.txt'
write_canonical makes sure that Prolog can read the output back into the same exact atom.
Your problem seems to be that you do not correctly represent the path in Prolog. If the path comes from an external source, you first need to escape it (add a backslash in front of every backslash) before you can store it as a Prolog atom.
Say I have a field on a datawindow that is the value of a database column ("Insert > Column). It has conditions in which it needs to be protected (Properties>General>Protect).
I want to have the field background grey when it's protect. At the moment, the only way I can work out how to do this is to copy the protect conditional, no matter how complex, substituting the 1 (protect) and 0 (not protect) for colour values.
Is there some sort of syntax I can use in the Expression field for the column's background colour that references the protect value of the column? I tried
if (column.protect=1, Grey, White)
but it returns errorous saying it expects a TRUE/FALSE condition.
Is what I'm after impossible, or is it just a matter of getting the right syntax.
Cheers.
Wow. You like complex, layered questions.
The first problem is accessing the value, which isn't done as directly as you described. As a matter of fact, you use a Describe() to get the value. The only problem with that is that it comes back as a string in the following format, with quotes around (note that we're using standard PowerScript string notation where ~t is a tab)
"<DefaultValue>~t<Expression>"
You want the expression, so you'll have to parse it out, dropping the quotes as well.
Once you've got the expression, you'll need to evaluate it for the given row. That can be done with another Describe () call, particularly:
Describe ("Evaluate('<expression>', <rownum>)")
The row number that an expression is being evaluated on can be had with the GetRow() function.
This may sound like it needs PowerScript and some interim value storage, but as long as you're willing to make redundant function calls to get a given value more than once, you can do this in an expression, something like (for an example column b):
if (Describe ("Evaluate (~"" + Mid (Describe ("b.protect"),
Pos (Describe ("b.protect"), "~t")+1,
Len (Describe ("b.protect")) - Pos (Describe ("b.protect"), "~t") - 1)
+ "~", " + String (GetRow()) + ")")='1',
rgb(128, 128, 128),
rgb(255,255,255))
This looks complex, but if you put the Mid() expression in a compute field so you can see the result, you'll see that simply parses out the Protect expression and puts it into the Describe (Evaluate()) syntax described above.
I have put one cheat into my code for simplicity. I used the knowledge that I only had single quotes in my Protect expression, and chose to put the Evaluate() expression string in double quotes. If I was trying to do this generically for any column, and couldn't assume an absence of double quotes in my Protect expression, I'd have use a global function to do a replace of any double quotes in the Protect expression with escaped quotes (~"), which I believe in your code would look like a triple tilde and a quote. Then again, if I had to make a global function call (note that global function calls in expressions can have a significant performance impact if there are a lot of rows), I'd just pass it the Describe ("column.protect") and GetRow() and build the entire expression in PowerScript, which would be easier to understand and maintain.
Good luck,
Terry.