Vocabulary/squarelf

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[ y

Same

Rank Infinity -- operates on x and y as a whole -- WHY IS THIS IMPORTANT?

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Returns noun y unchanged: [y is equivalent to y.

   z=: i.6          NB. try any noun here
   assert z -: [z

NOTE: Same (] y) is equivalent to ([ y)

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Common uses

See Same (]), which is conventionally the one used in this role.

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Related Primitives

Same (] y)

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Use These Combinations

Combinations using [ y that have exceptionally good performance include:

What it does	Type; Precisions; Ranks	Syntax	Variants; Restrictions	Benefits; Bug Warnings
Extract substring/subarray	table or list	x ];.0 y	or [;.0	avoids creating indexes
Reshape infixes		x ]\ y	[ , in place of ]

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x [ y

Left

Rank Infinity -- operates on x and y as a whole -- WHY IS THIS IMPORTANT?

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Returns the (noun) value of x

   x=: 3
   y=: 5
   x [ y
3
   assert x -: x [ y   NB. try with any 2 nouns as x and y

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Common uses

1. Separate two assignments on the same line

The right-hand phrase must evaluate to a noun, to represent a valid y for use in (x [ y).

   p=: 3 [ q=: 5

2. In a dyadic tacit verb: bring in the value of argument x

   13 : 'x+(x-y)*y'
[ + - * ]

3. In a dyadic tacit verb: use u@[ to execute u on the x argument to a verb

   3 (< , <) 'a'       NB. No good: the , are executed as dyads
|domain error
   3 (<@[ , <@]) 'a'   NB. Execute as monads on the appropriate argument
+-+-+
|3|a|
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Related Primitives

Right (x ] y)

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Use These Combinations

Combinations using [ y that have exceptionally good performance include:

What it does	Type; Precisions; Ranks	Syntax	Variants; Restrictions	Benefits; Bug Warnings
Extract substring/subarray	table or list	x ];.0 y	or [;.0	avoids creating indexes
Fetch from multiple index lists (each row of x is one index list into y)		x (<"1@[ { ]) y		avoids boxing x

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