Given the following transcript:
```ucm:hide
.> pull https://github.com/unisonweb/base:v3:.releases._latest .base
```
```unison
foo = List.map (x -> x * 2) [1,2,3]
```
```ucm
.> add foo
.> view foo
```
When this is executed, I get the following output:
```unison
foo = List.map (x -> x * 2) [1,2,3]
```
```ucm
I found and typechecked these definitions in scratch.u. If you
do an `add` or `update`, here's how your codebase would
change:
⍟ These new definitions are ok to `add`:
foo : [Nat]
```
```ucm
.> add foo
⍟ I've added these definitions:
foo : [Nat]
.> view foo
foo : [Nat]
foo =
use Nat *
List.map (x -> x * 2) [1, 2, 3]
```
I understand why it is this way but is there an alternative approach that would show the computed value of foo (i.e. [2, 4, 6]), as if we're working in a scratch.u file?
I also tried:
```ucm
.> foo
```
But get the error I don't know how to foo..
Yes, try display foo. :)
The naming is a bit weird. We keep thinking of renaming view to source, and then maybe leave display (or rename it to eval and allow arbitrary expressions, like a REPL).
Related
Using list comprehension, elixir allow do pattern matching like that:
iex()> for {a,2,c} = ch <- [{1,2,3},{4,5,6},3,4,5], do: c
[3]
But when I'm trying to do something like that with binary, I fail:
iex()> for << b1::size(2), b2::size(3), b3::size(3) >> = <<ch>> <- 'hello', do: b1
[]
Nevertheless, it matches well when standalone:
<< b1::size(2), b2::size(3), b3::size(3) >> = <<100>>
"d"
iex(282)> b2
4
iex(283)> b1
1
iex(284)> b3
4
It also works well when I pass mattern matching clause as secornd parameter to for:
iex(286)> for ch <- 'hello', << b1::size(2), b2::size(3), b3::size(3) >> = <<ch>>, do: b1
[1, 1, 1, 1, 1]
I'm interested if it possible to do something like first example with binary.
This is what fails:
<<ch>> <- 'hello'
In your very first example you do var <- list and later you try <<var>> <- list which is not the same by all means.
'hello' is the list of integers in the first place. Check this:
[104,101,108,108,111]
#⇒ 'hello'
Kernel.SpecialForms.for/1 is iterating through the list, one by one. One cannot match binary to an integer as is:
<<_::size(2), _::size(3), _::size(3)>> = 101
#⇒ ** (MatchError) no match of right hand side value: 101
And also:
<<ch>> = 101
#⇒ ** (MatchError) no match of right hand side value: 101
The latter code example from your question works because you match to an integer and then explicitly tell to Elixir/Erlang it’s to be treated as binary by wrapping it with << >>:
<<b1::size(2), _::size(3), _::size(3)>> = <<101>>
#⇒ "e"
Looking to extract records from a table in a very well formed HTMl table using HXT. I've reviewed a couple of examples on SO and the HXT documentation, such as:
Extracting Values from a Subtree
http://adit.io/posts/2012-04-14-working_with_HTML_in_haskell.html
https://www.schoolofhaskell.com/school/advanced-haskell/xml-parsing-with-validation
Running Haskell HXT outside of IO?
extract multiples html tables with hxt
Parsing html in haskell
http://neilbartlett.name/blog/2007/08/01/haskell-explaining-arrows-through-xml-transformationa/
https://wiki.haskell.org/HXT/Practical/Simple2
https://wiki.haskell.org/HXT/Practical/Simple1
Group html table rows with HXT in Haskell
Parsing multiple child nodes in Haskell with HXT
My problem is:
I want to identify a table uniquely by a known id, and then for each
tr within that table, create a record object and return this as a list
of records.
Here's my HTML
<!DOCTYPE html>
<head>
<title>FakeHTML</title>
</head>
<body>
<table id="fakeout-dont-get-me">
<thead><tr><td>Null</td></tr></thead>
<tbody><tr><td>Junk!</td></tr></tbody>
</table>
<table id="Greatest-Table">
<thead>
<tr><td>Name</td><td>Favorite Rock</td></tr>
</thead>
<tbody>
<tr id="rock1">
<td>Fred</td>
<td>Igneous</td>
</tr>
<tr id="rock2">
<td>Bill</td>
<td>Sedimentary</td>
</tr>
</tbody>
</table>
</body>
</html>
Here's the code I'm trying, along with 2 different approaches to parsing this. First, imports ...
{-# LANGUAGE Arrows, OverloadedStrings, DeriveDataTypeable, FlexibleContexts #-}
import Text.XML.HXT.Core
import Text.HandsomeSoup
import Text.XML.HXT.XPath.XPathEval
import Data.Tree.NTree.TypeDefs
import Text.XML.HXT.XPath.Arrows
What I want is a list of Rockrecs, eg from...
recs = [("rock1", "Name", "Fred", "Favorite Rock", "Igneous"),
("rock2", "Name", "Bill", "Favorite Rock", "Sedimentary")]
data Rockrec = Rockrec { rockID:: String,
rockName :: String,
rockFav :: String} deriving Show
rocks = [(\(a,_,b,_,c) -> Rockrec a b c ) r | r <- recs]
-- [Rockrec {rockID = "rock1", rockName = "Fred", rockFav = "Igneous"},
-- Rockrec {rockID = "rock2", rockName = "Bill", rockFav = "Sedimentary"}]
Here's my first way, which uses a bind on runLA after I return a bunch of [XMLTree]. That is, I do a first parse just to get the right table, then I process the tree rows after that first grab.
Attempt 1
getTab = do
dt <- Prelude.readFile "fake.html"
let html = parseHtml dt
tab <- runX $ html //> hasAttrValue "id" (== "Greatest-Table")
return tab
-- hmm, now this gets tricky...
-- table <- getTab
node tag = multi (hasName tag)
-- a la https://stackoverflow.com/questions/3901492/running-haskell-hxt-outside-of-io?rq=1
getIt :: ArrowXml cat => cat (Data.Tree.NTree.TypeDefs.NTree XNode) (String, String)
getIt = (node "tr" >>>
(getAttrValue "id" &&& (node "td" //> getText)))
This kinda works. I need to massage a bit, but can get it to run...
-- table >>= runLA getIt
-- [("","Name"),("","Favorite Rock"),("rock1","Fred"),("rock1","Igneous"),("rock2","Bill"),("rock2","Sedimentary")]
This is a second approach, inspired by https://wiki.haskell.org/HXT/Practical/Simple1. Here, I think I'm relying on something in {-# LANGUAGE Arrows -} (which coincidentally breaks my list comprehension for rec above), to use the proc function to do this in a more readable do block. That said, I can't even get a minimal version of this to compile:
Attempt 2
getR :: ArrowXml cat => cat XmlTree Rockrec
getR = (hasAttrValue "id" (== "Greatest-Table")) >>>
proc x -> do
rockId <- getText -< x
rockName <- getText -< x
rockFav <- getText -< x
returnA -< Rockrec rockId rockName rockFav
EDIT
Trouble with the types, in response to the comment below from Alec
λ> getR [table]
<interactive>:56:1-12: error:
• Couldn't match type ‘NTree XNode’ with ‘[[XmlTree]]’
Expected type: [[XmlTree]] -> Rockrec
Actual type: XmlTree -> Rockrec
• The function ‘getR’ is applied to one argument,
its type is ‘cat0 XmlTree Rockrec’,
it is specialized to ‘XmlTree -> Rockrec’
In the expression: getR [table]
In an equation for ‘it’: it = getR [table]
λ> getR table
<interactive>:57:1-10: error:
• Couldn't match type ‘NTree XNode’ with ‘[XmlTree]’
Expected type: [XmlTree] -> Rockrec
Actual type: XmlTree -> Rockrec
• The function ‘getR’ is applied to one argument,
its type is ‘cat0 XmlTree Rockrec’,
it is specialized to ‘XmlTree -> Rockrec’
In the expression: getR table
In an equation for ‘it’: it = getR table
END EDIT
Even if I'm not selecting elements, I can't get the above to run. I'm also a little puzzled at how I should do something like put the first td in rockName and the second td in rockFav, how to include an iterator on these (supposing I have a lot of td fields, instead of just 2.)
Any further general tips on how to do this more painlessly appreciated.
From HXT/Practical/Google1 I think I am able to piece together a solution.
{-# LANGUAGE Arrows #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Hanzo where
import Text.HandsomeSoup
import Text.XML.HXT.Cor
atTag tag =
deep (isElem >>> hasName tag)
text =
deep isText >>> getText
data Rock = Rock String String String deriving Show
rocks =
atTag "tbody" //> atTag "tr"
>>> proc x -> do
rowID <- x >- getAttrValue "id"
name <- x >- atTag "td" >. (!! 0) >>> text
kind <- x >- atTag "td" >. (!! 1) >>> text
returnA -< Rock rowID name kind
main = do
dt <- readFile "html.html"
result <- runX $ parseHtml dt
//> hasAttrValue "id" (== "Greatest-Table")
>>> rocks
print result
The key takeways are these:
Your arrows work on streams of elements, but not individual elements. This is the ArrowList constraint. Thus, calling getText three times will produce surprising behavior because getText represents all the different possible text values you could get in the course of streaming <table> elements through your proc x -> do {...}.
What we can do instead is focus on the stream we want: a stream of <tr>s inside the <tbody>. For each table row, we grab the ID attribute value and the text of the first two <td>s.
This does not seem the most elegant solution, but one way we can index into a stream is to filter it down with the (>.) :: ArrowList cat => cat a b -> ([b] -> c) -> cat a c combinator.
One last trick, one that I noticed in the practical wiki examples: we can use deep and isElem/isText to focus on just the nodes we want. XML trees are noisy!
I have a struct in Octave that contains some big arrays.
I'd like to know the names of the fields in this struct without having to look at all these big arrays.
For instance, if I have:
x.a=1;
x.b=rand(3);
x.c=1;
The obvious way to take a gander at the structure is as follows:
octave:12> x
x =
scalar structure containing the fields:
a = 1
b =
0.7195967 0.9026158 0.8946427
0.4647287 0.9561791 0.5932929
0.3013618 0.2243270 0.5308220
c = 1
In Matlab, this would appear as the more succinct:
>> x
x =
a: 1
b: [3x3 double]
c: 1
How can I see the fields/field names without seeing all these big arrays?
Is there a way to display a succinct overview (like Matlab's) inside Octave?
Thanks!
You might want to take a look at Basic Usage & Examples. There's several functions mentioned that sound like they'll control the displaying in the terminal.
struct_levels_to_print
print_struct_array_contents
These two functions sound like they're do what you want. I tried both and couldn't get the 2nd one to work. The 1st function changed the terminal output like so:
octave:1> x.a=1;
octave:2> x.b=rand(3);
octave:3> x.c=1;
octave:4> struct_levels_to_print
ans = 2
octave:5> x
x =
{
a = 1
b =
0.153420 0.587895 0.290646
0.050167 0.381663 0.330054
0.026161 0.036876 0.818034
c = 1
}
octave:6> struct_levels_to_print(0)
octave:7> x
x =
{
1x1 struct array containing the fields:
a: 1x1 scalar
b: 3x3 matrix
c: 1x1 scalar
}
I'm running a older version of Octave.
octave:8> version
ans = 3.2.4
If I get a chance I'll check that other function, print_struct_array_contents, to see if it does what you want. Octave 3.6.2 looks to be the latest version as of 11/2012.
Use fieldnames ()
octave:33> x.a = 1;
octave:34> x.b = rand(3);
octave:35> x.c = 1;
octave:36> fieldnames (x)
ans =
{
[1,1] = a
[2,1] = b
[3,1] = c
}
Or you you want it to be recursive, add the following to your .octaverc file (you may want to adjust it to your preferences)
function displayfields (x, indent = "")
if (isempty (indent))
printf ("%s: ", inputname (1))
endif
if (isstruct (x))
printf ("structure containing the fields:\n");
indent = [indent " "];
nn = fieldnames (x);
for ii = 1:numel(nn)
if (isstruct (x.(nn{ii})))
printf ("%s %s: ", indent, nn{ii});
displayfields (x.(nn{ii}), indent)
else
printf ("%s %s\n", indent, nn{ii})
endif
endfor
else
display ("not a structure");
endif
endfunction
You can then use it in the following way:
octave> x.a=1;
octave> x.b=rand(3);
octave> x.c.stuff = {2, 3, 45};
octave> x.c.stuff2 = {"some", "other"};
octave> x.d=1;
octave> displayfields (x)
x: structure containing the fields:
a
b
c: structure containing the fields:
stuff
stuff2
d
in Octave, version 4.0.0 configured for "x86_64-pc-linux-gnu".(Ubuntu 16.04)
I did this on the command line:
print_struct_array_contents(true)
sampleFactorList % example, my nested structure array
Output: (shortened):
sampleFactorList =
scalar structure containing the fields:
sampleFactorList =
1x6 struct array containing the fields:
var =
{
[1,1] = 1
[1,2] =
2 1 3
}
card =
{
[1,1] = 3
[1,2] =
3 3 3
}
To disable/get back to the old behaviour
print_struct_array_contents(false)
sampleFactorList
sampleFactorList =
scalar structure containing the fields:
sampleFactorList =
1x6 struct array containing the fields:
var
card
val
I've put this print_struct_array_contents(true) also into the .octaverc file.
I am interested in using the monotone spline, but I get an error when R tries to use it. I am using R 2.12.0, and the method 'monoH.FC' says that it has been supported since 2.8.0
Reproducible example (same result for more complicated (x,y) relationships)
x<-1:2
y<-1:2
spline(x,y,method="monoH.FC")
Error in spline(x, y, method = "monoH.FC") : invalid interpolation method
What I have tried
?spline returns:
...
Usage:
...
spline(x, y = NULL, n = 3*length(x), method = "fmm",
xmin = min(x), xmax = max(x), xout, ties = mean)
...
Arguments:
method: specifies the type of spline to be used. Possible values are
‘"fmm"’, ‘"natural"’, ‘"periodic"’ and ‘"monoH.FC"’.
...
But the spline function itself indicates that the 'monoH.FC' method is not supported:
...
method <- pmatch(method, c("periodic", "natural", "fmm"))
if (is.na(method))
stop("invalid interpolation method")
...
Question
How can I use method = 'monoH.FC' with spline?
Use splinefun; it supports method=monoH.FC.
The last example in ?spline shows you how to do it.
## An example of monotone interpolation
n <- 20
set.seed(11)
x. <- sort(runif(n)) ; y. <- cumsum(abs(rnorm(n)))
plot(x.,y.)
curve(splinefun(x.,y.)(x), add=TRUE, col=2, n=1001)
curve(splinefun(x.,y., method="mono")(x), add=TRUE, col=3, n=1001)
legend("topleft", paste("splinefun( \"", c("fmm", "monoH.CS"), "\" )", sep=''),
col=2:3, lty=1)
Let's say I have an R function in which the arguments can be a one of a few predefined named values (one of which is the default) or a custom character vector. How should I implement this without relying on magic value names or another flag?
#allow use of predefined subsets or pass their own list
bratPack<-function(members='CORE',...){
if (members=='CORE')
members<-c('Emilio Estevez','Anthony Michael Hall','Rob Lowe','Andrew McCarthy','Demi Moore','Judd Nelson','Molly Ringwald','Ally Sheedy')
else if (members=='ALL')
members<-c('Emilio Estevez','Anthony Michael Hall','Rob Lowe','Andrew McCarthy','Demi Moore','Judd Nelson','Molly Ringwald','Ally Sheedy','James Spader','Robert Downey, Jr.','Jon Cryer', 'John Cusack', 'Kevin Bacon', 'Jami Gertz', 'Mary Stuart Masterson', 'Matthew Broderick', 'Sean Penn', 'Kiefer Sutherland')
...
}
From your example we have the choice of "CORE" and "ALL". If those are the two options, then we specify them in the function definition for the argument 'members'. E.g.:
foo <- function(x, members = c("CORE", "ALL")) {
## do something
}
That function definition sets up the allowed values for argument 'members', with a default of "CORE" as this is the first named option.
The code that one uses within the function body is match.arg(), as #Joris has already mentioned, but because we have set the function up as above, we can simply the usage to just match.arg(members).
So we can write foo as:
foo <- function(x, members = c("CORE", "ALL")) {
## evaluate choices
members <- match.arg(members)
## do something
print(members)
}
Which we use like this:
> foo()
[1] "CORE"
> foo(members = "CORE")
[1] "CORE"
> foo(members = "ALL")
[1] "ALL"
> foo(members = "3rdRate")
Error in match.arg(members) : 'arg' should be one of “CORE”, “ALL”
Notice the behaviour when we supply an string not included in the set of options. We get an intuitive error message, all because we set up the options in the function arguments.
I'd use some constant dataframe somewhere in the package:
.mdata <- data.frame(
CORE= c(TRUE,FALSE,TRUE),
OLD = c(TRUE,TRUE,FALSE),
ALL = c(TRUE,TRUE,TRUE),
row.names=c("John Doe", "Jan Janssen", "Piet Peters")
)
bratPack<-function(members='CORE',...){
m.tmp <- try(
match.arg(members,names(.mdata),several.ok=T),
silent=T)
if(!is(m.tmp,"try-error"))
members <- rownames(.mdata)[.mdata[[members]]]
print(members)
}
> bratPack('CORE')
[1] "John Doe" "Piet Peters"
> bratPack('Jan Janssen')
[1] "Jan Janssen"
> bratPack(c("John Doe","Dick Dickers"))
[1] "John Doe" "Dick Dickers"