I-Beam

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I-Beam () is a primitive ambivalent function or monadic operator that takes a numeric code as an argument/operand and provides a range of ad-hoc operations. This range covers non-primitive functions, for example experimental features, interpreter-level control, access to the environment, and information about APL itself.

History

I-Beam was introduced in APL\360 as an ambivalent function for implementers to execute IBM System/360 (I-Beam being pronounced very similarly to IBM) instructions from program control. The convenience of this lead to I-Beam becoming directly available for use by anyone.[1] However, modern IBM-derived APLs replace all I-Beams with quad names. For example, 5⌶ became ⎕DL (Delay) while changing time unit from jiffies of 1⁄300th of a second to a whole second.

Later, after it became common to use arrays as operands, Dyalog APL 12.1 began using the glyph as an operator where the operand selects functionality. It is used for testing experimental features, some of which may eventually become primitives or quad names. For example, 819⌶ became ⎕C (Case Convert), while introducing distinction between case folding (for case insensitive comparisons) and case mapping (for human presentation forms).

Mnemonics

In general, I-Beam's numeric operand isn't intended to be easily recalled. But some are given meaningful names.

One method is to devise a name from the Roman numeral letters I, V, X, L, C, D, and M:[2]

I-Beam Numeral
Colour Coding CC (200)
Colour Coding Information CCI (201)
Called Monadically CM (900)
Line Count LC (50100)

External links

References

APL built-ins [edit]
Primitives (Timeline) Functions
Scalar
Monadic ConjugateNegateSignumReciprocalMagnitudeExponentialNatural LogarithmFloorCeilingFactorialNotPi TimesRollTypeImaginarySquare Root
Dyadic AddSubtractTimesDivideResiduePowerLogarithmMinimumMaximumBinomialComparison functionsBoolean functions (And, Or, Nand, Nor) ∙ GCDLCMCircularComplexRoot
Non-Scalar
Structural ShapeReshapeTallyDepthRavelEnlistTableCatenateReverseRotateTransposeRazeMixSplitEncloseNestCut (K)PairLinkPartitioned EnclosePartition
Selection FirstPickTakeDropUniqueIdentityStopSelectReplicateExpandSet functions (IntersectionUnionWithout) ∙ Bracket indexingIndexCartesian ProductSort
Selector Index generatorGradeIndex OfInterval IndexIndicesDealPrefix and suffix vectors
Computational MatchNot MatchMembershipFindNub SieveEncodeDecodeMatrix InverseMatrix DivideFormatExecuteMaterialiseRange
Operators Monadic EachCommuteConstantReplicateExpandReduceWindowed ReduceScanOuter ProductKeyI-BeamSpawnFunction axis
Dyadic BindCompositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner ProductDeterminantPowerAtUnderRankDepthVariantStencilCutDirect definition (operator)
Quad names Index originComparison toleranceMigration levelAtomic vector