Playground
The J Playground runs an interactive J session.
To try it out, Click Here, or use the link in the wiki menu on the left.
There are two windows: Term, an interactive console, and Edit, a script editor. The windows can be resized and flipped to be stacked vertically.
Term
The Term window lets you type in and run J expressions.
- if the cursor is on the last line of the display, press Enter to execute it.
- if the cursor is on a line above the last line of the display, press Enter to copy it to the end of the display. You can then edit it and press Enter to execute it.
The window can be edited as you wish, for example to delete unwanted output.
The input log can be accessed either
- by pressing the Ctrl+Shift up/down cursor keys. This steps through the inputs.
- by pressing Ctrl+D or selecting menu View|Input Log. This shows a popup menu, where selecting an entry copies it to the end of the display.
Edit
The Edit window is for entering one or more J expressions for later execution.
You can select from the Examples menu to populate the Edit window with typical expressions, or enter your own expressions.
To run the current line, put the cursor on it and press Ctrl+Enter or Ctrl+Shift+Enter. The difference is that when the expression is an assignment, Ctrl+Enter has no output while Ctrl+Shift+Enter displays the assigned value.
You can run through all the J expressions in a window by holding down Ctrl or Ctrl+Shift and repeatedly pressing Enter. Alternatively, select menu Edit Run|All Lines.
If the current line starts a multi-line definition, the entire definition is read in.
Context Sensitive
Context sensitive help is available for J language primitives.
In either window, select the primitive, or put the cursor inside or to the left of a primitive. Press Ctrl+F1 for the vocabulary definition.
For example, with the cursor inside i. this will show the definition of Integers.
Also, in the Term window, put the cursor spaced out to the left or right of an expression, then press Ctrl+F1 to output J word formation on the line, e.g.
2 3 4 +/ i. 5 ┌─────┬─┬─┬──┬─┐ │2 3 4│+│/│i.│5│ └─────┴─┴─┴──┴─┘
Tips & Tricks
File handling
Standard library file handling verbs can be used, like dir, freads and fwrites. They operate on a temporary virtual filesystem that is isolated from the host filesystem, and lost when refreshing the page. Files can be loaded into the editor using Edit_plj_ for editing or copy-pasting elsewhere. Do note this might, without warning, overwrite any changes in the Editor. Edit_plj_ gets the content from the Editor into J when used monadically, and sets the content (overwriting the previous content without warning), when used dyadically. For instance:
dir '~addons/math/misc/'
amoeba.ijs 7730 21-Aug-24 21:25:41
bigpi.ijs 501 21-Aug-24 21:25:41
brent.ijs 1799 21-Aug-24 21:25:41
build.ijs 138 21-Aug-24 21:25:41
cheby.ijs 2073 21-Aug-24 21:25:41
contfrac.ijs 814 21-Aug-24 21:25:41
det.ijs 444 21-Aug-24 21:25:41
fermat.ijs 851 21-Aug-24 21:25:41
gamesolver.ijs 2598 21-Aug-24 21:25:41
gcd.ijs 711 21-Aug-24 21:25:41
integer.ijs 2332 21-Aug-24 21:25:41
integrat.ijs 2879 21-Aug-24 21:25:41
jacobi.ijs 1387 21-Aug-24 21:25:41
legendre.ijs 1087 21-Aug-24 21:25:41
linear.ijs 4833 21-Aug-24 21:25:41
makemat.ijs 2266 21-Aug-24 21:25:41
manifest.ijs 1795 21-Aug-24 21:25:41
matfacto.ijs 3376 21-Aug-24 21:25:41
mathutil.ijs 886 21-Aug-24 21:25:41
matutil.ijs 3337 21-Aug-24 21:25:41
mean.ijs 431 21-Aug-24 21:25:41
... NB. output shortened for brevity
Edit_plj_~ freads '~addons/math/misc/mean.ijs' NB. load mean.ijs in the Editor
'~addons/math/misc/mean.ijs' fwrites~ Edit_plj_'' NB. After editing, save the file back in place (for this session only).
freads '~addons/math/misc/mean.ijs' NB. read back changed file.
NB. math/misc/mean
NB. Various means
NB. version: 1.0.0
NB. arithmean arithmetic mean
NB. geomean geometric mean
NB. harmean harmonic mean
NB. commonmean common mean
NB.*arithmean v Arithmetic mean of y
arithmean=: +/ % #
NB.*geomean v Geometric mean of y
geomean=: # %: */
NB.*harmean v Harmonic mean of y
harmean=: arithmean &. (%"_)
NB.*commonmean v Common mean of y
commonmean=: {. @ ((geomean,arithmean) ^: _)
NB. I added this line in the Playground editor
Of course, written files do not remain, but are reset after reloading the web page.
Graphics
The J Playground lets you make nice plots, which are rather small for more complex plots or multi-plots. You can set the resolution of the plot canvas by e.g.
load'plot' CANVAS_DEFSIZE_jzplot_ 400 200 CANVAS_DEFSIZE_jzplot_=:600 400 plot _6 6;'sin'
Viewmat is also supported, but sometimes triggers the following error:
|assertion failure: enclength | (0<:ex)*.(30>:ex) |[-0]
This can be prevented by redefining enclength_jzlib_ as follows to increase the upper limit the assertion fails on:
enclength_jzlib_=: 3 : 0
ix=. <: +/({:"1 lz_length)<:y
code=. 257 + ix
ex=. y-(<ix,1){lz_length
assert. (0<:ex)*.(300>:ex) NB. upped limit from 30 to 300 here.
code, 1000+ex
)