J Language Changelog

What's new in J Language 901

• Summary of Changes to the J Language in the release
• Language addition: gerund"r: the left operand of m"v can now be a cyclic gerund, giving a sequence of verbs to be applied to corresponding cells of the arguments. At long last you can apply a different verb to each cell of a noun. For compatibility with the older uses of m"n, the gerund is recognized only if the ranks v are not all infinite and m is a list of boxes containing a valid gerund. This is an incompatible change only if you used m"n with finite rank and an m that looked like a gerund. In that case, you need to replace m"n with m"_"n.
• Language change: Scatter-amend support: x m} y changed when m is a numeric array of rank>1. In that case, each 1-cell of m is the index list of a cell of y that is replaced by the corresponding cell of x. This is an incompatible change with J8.07 and earlier, but is compatible with previous J9.01 betas.
• Language addition: New primitives for iteration: A family of primitives implements Fold, as previously proposed. Features:
• iteration can be forward or backward through items of a noun
• initial value provided as its own argument
• early termination allowed
• either one result for the whole iteration or a result item per iteration
• result of an iteration can be a subset of the complete internal state passed to the next iteration
• results of individual iterations can be put into the overall result or not
• iteration can be by item or on the entire argument until a condition is met
• Language addition: : u. and v. are added to mean 'u/v in the calling context'. They are implied locatives, carrying with them the private namespace and implied locale at the time the operands they represent were created. When they are executed, the execution occurs in the original name environment. This long-awaited change allows you to pass a private name from an explicit definition into an explicit modifier, and when the modifier executes its u./v. operand, the execution happens as if it were executed at the point just before the modifier was called.
• Language addition: Foreigns to set script name: 4!:6 y adds an entry to the table of script names returned by 4!:3; 4!:7 y sets the script number to use for subsequent assignments.
• New control over precision of numeric constants:
• No numeric constant containing a period will be demoted to lower than floating-point precision (thus 2. or 2.0 is a float value)
• no number of more than one character will be demoted below integer precision (thus, 01 is an integer value).
• No numeric constant containing 'j' will be demoted below complex precision (thus, 1j0 is a complex value).
• No numeric constant containing 'r' will be demoted below rational precision (thus, 2r1 is a rational value).
• This makes it easier to create DLL inputs of the correct precision, and to make the datatype of constants match that of other nouns they operate with. Linear representations preserve the distinction between precisions.
• If an adverb/conjunction with only one defined valence refers to any of m n u v and also to x, the defined valence will be construed as dyadic. Example:
• 1 : 'x u y'
• Formerly this would give domain error when executed as a dyad, or value error when executed as a monad. This is an incompatible change only if you used the variable x in a monadic adverb/conjunction. In that case, use a different name, or add a nonempty dyadic case to the end of your definition.
• Quicker way to specify numbered locales: numbered locales can be referred to by indirect locatives that are an integer atom or a boxed integer atom (rather than a boxed string). Such locatives can be processed quicker because they do not have to be validated and converted to a number. If you have (obj =: conew parameters) you can replace that with (obj =: 0&".@> conew parameters) and get a performance improvement every time you use (name__obj).
• Domain of x u;.0 y expanded: the selected subarray may start on any valid atom of its axis, or on the atom one position before or after the axis. In all cases the length will be limited to the largest valid value for the starting position (which will be 0 for positions starting outside the array)
• Domain of {:: extended: 0 {:: y now returns > y rather than length error when y is an atom.
• Language deletion: primitive conjunctions .. and .: (Even and Odd) are removed from the language
• Language deletion: calculus primitives (d. D. D:) are removed from the language, replaced by a J addon math/calculus that provides most of the functionality
• Language deletion: Taylor-series primitives (t. t: T.) are removed from the language
• At the end of a for_xyz. loop, the names xyz and xyz_index remain defined. If the loop was exited by break. or goto., the names simply retain their latest values. If the loop is exited by executing all the iterations, xyz is set to an empty list and xyz_index is set to the number of iterations that were executed.
• else. is now allowed as the last alternative in an if. control, even if there has been a previous elseif.