A special form is a kind of verb that can perform specialized operations like control flow and global modification. Special forms are generally polyadic (more than 2 arguments).
You have already seen one special form: If ($[;;..]). We will be covering the rest of these special forms in this chapter.
Given array x, indices y and monadic function z, Amend will apply z to the elements at indices y.
@["ABC";1 2;_:]
"Abc"
This is useful when you don't want to use assignment to modify specific elements in an array.
Same as 3 argument amend, but z is dyadic, and u is the second argument provided to z.
@[2 3;0;+;4]
6 3
Similar to amend, x is an array, but y is a single multidimensional index, and z is a monadic function.
Similar to 3 arguments, but with z dyadic, and u as the second argument.
An error handling mechanism.
x is a function, y is an array of arguments to x, and z is the function that is applied to the error message (see ch 11), if x.y fails.
Otherwise returns x.y. Try is most useful when you are in deeper levels of nesting in a function, and print debugging with \ (trace) is not
completely helpful.
.[+;1 2;"E:",]
3
.[+;1,`2;"E:",]
"E:'limit\n"
Splices an array z between the indices given in y in array x. A very useful string function.
?["abcd";1 3;"xyz"]
"axyzd"