Migration level

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Migration level (⎕ML, )EvLevel, ⎕CS), Evolution level, or Compatibility setting is a number that, in Dyalog APL, APL+Win, and APLX respectively, specifies exact behaviour relative to APL2. In Dyalog APL and APL+Win, a lower value represents a behaviour closer to the original NARS specification, while a higher the value represents a behaviour closer to APL2. In APLX, a lower value matches APL2 while a higher value indicates higher backwards compatibility with APL.68000.

APL+Win settings

APL+Win's default is )EvLevel 2.

Feature )EvLevel 0 )EvLevel 1 )EvLevel 2
Dyadic ⊂ EVOLUTION ERROR Partitioned Enclose Partition
Monadic ↓ EVOLUTION ERROR Split SYNTAX ERROR
Monadic ∊ EVOLUTION ERROR Type Enlist
Monadic ↑ EVOLUTION ERROR Mix First
Monadic ⊃ EVOLUTION ERROR First Mix
Bracket indexing of a strand EVOLUTION ERROR indexing applied to strand as a whole EVOLUTION ERROR
Unparenthesised strand assignment EVOLUTION ERROR assigned value distributed to names EVOLUTION ERROR
(/) EVOLUTION ERROR Replicate function EVOLUTION ERROR
(\) EVOLUTION ERROR Expand function EVOLUTION ERROR

Work-arounds

APL+Win provides system function alternatives to the functions that are affected by moving to evolution level 2:

Partitioned Enclose ⎕PENCLOSE
Split ⎕SPLIT
Type ⎕TYPE
Mix ⎕MIX
First ⎕FIRST
Replicate function ⎕REPL
Expand function ⎕EXPAND

Dyalog settings

Dyalog APL currently offers the following settings:

⎕ML=0 Z←∊R Monadic ∊ is interpreted as Type rather than Enlist.
⎕ML=1 Default behaviour
⎕ML≥2 Z←↑R Monadic ↑ is interpreted as First rather than Mix.
Z←⊃R Monadic ⊃ is interpreted as Mix rather than First.
Z←≡R Monadic ≡ returns a positive rather than a negative value, if its argument has non-uniform depth.
⎕ML=3 R←X⊂[K]Y Dyadic ⊂ is interpreted as Partition (⊆) rather than Partitioned Enclose.
⎕TC The order of the elements of ⎕TC is the same as in APL2.

Work-arounds

When migrating to Dyalog APL, the below drop-ins for the affected built-ins allow setting ⎕ML←1 while preserving code behaviour. It is then safe to programmatically (as shown in the rightmost column) change all occurrences of the affected built-ins with their respective covers.

Migrating from Define Then run this on all code
⎕ML=0 
Epsilon←{×⎕NC'⍺':⍺∊⍵ ⋄ ⊃0⍴⊂⍵}
 '''[^'']+''' '∊'⎕R'&' 'Epsilon'
⎕ML=2 
UpArrow←{×⎕NC'⍺':⍺↑⍵ ⋄ ⊃⍵}
RightShoe←{×⎕NC'⍺':⍺↑⍵ ⋄ ↑⍵}
EqualUnderbar←|≡
 '''[^'']+''' '↑' '⊃' '≡'⎕R'&' 'UpArrow' 'RightShoe' 'EqualUnderbar'
⎕ML=3 
UpArrow←{×⎕NC'⍺':⍺↑⍵ ⋄ ⊃⍵}
RightShoe←{×⎕NC'⍺':⍺↑⍵ ⋄ ↑⍵}
EqualUnderbar←(|≡)
LeftShoe←{×⎕NC'⍺':⍺⊆⍵ ⋄ ⊂⍵}
quadTC←(⎕UCS 8 13 10)
 '''[^'']+''' '↑' '⊃' '≡' '⊂' '⎕TC'⎕R'&' 'UpArrow' 'RightShoe' 'EqualUnderbar' 'LeftShoe' ' quadTC'

Alternatively, the definitions can be used directly inside the text substitutions, whereby one avoids polluting existing code with these cover names.

APLX settings

APLX treats the value as a collection of individual bits, thus allowing the combination of an exact set of behaviours:

⎕CS←1 Stranding is done before bracket indexing
⎕CS←2 The name class of an invalid name is 4 rather than ¯1.
⎕CS←4 Format (⍕) and default output uses the same width for all columns, rather than determining the width separately for each column.

External links

Documentation

APL built-ins [edit]
Primitives (Timeline) Functions
Scalar
Monadic Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
Dyadic Add ∙ Subtract ∙ Times ∙ Divide ∙ Residue ∙ Power ∙ Logarithm ∙ Minimum ∙ Maximum ∙ Binomial ∙ Comparison functions ∙ Boolean functions (And, Or, Nand, Nor) ∙ GCD ∙ LCM ∙ Circular ∙ Complex ∙ Root
Non-Scalar
Structural Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Enlist ∙ Table ∙ Catenate ∙ Reverse ∙ Rotate ∙ Transpose ∙ Raze ∙ Mix ∙ Split ∙ Enclose ∙ Nest ∙ Cut (K) ∙ Pair ∙ Link ∙ Partitioned Enclose ∙ Partition
Selection First ∙ Pick ∙ Take ∙ Drop ∙ Unique ∙ Identity ∙ Stop ∙ Select ∙ Replicate ∙ Expand ∙ Set functions (Intersection ∙ Union ∙ Without) ∙ Bracket indexing ∙ Index ∙ Cartesian Product ∙ Sort
Selector Index generator ∙ Grade ∙ Index Of ∙ Interval Index ∙ Indices ∙ Deal ∙ Prefix and suffix vectors
Computational Match ∙ Not Match ∙ Membership ∙ Find ∙ Nub Sieve ∙ Encode ∙ Decode ∙ Matrix Inverse ∙ Matrix Divide ∙ Format ∙ Execute ∙ Materialise ∙ Range
Operators Monadic Each ∙ Commute ∙ Constant ∙ Replicate ∙ Expand ∙ Reduce ∙ Windowed Reduce ∙ Scan ∙ Outer Product ∙ Key ∙ I-Beam ∙ Spawn ∙ Function axis ∙ Identity (Null, Ident)
Dyadic Bind ∙ Compositions (Compose, Reverse Compose, Beside, Withe, Atop, Over) ∙ Inner Product ∙ Determinant ∙ Power ∙ At ∙ Under ∙ Rank ∙ Depth ∙ Variant ∙ Stencil ∙ Cut ∙ Direct definition (operator) ∙ Identity (Lev, Dex)
Quad names Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
APL glyphs [edit]
Information Glyph ∙ Typing glyphs (on Linux) ∙ Unicode ∙ Fonts ∙ Mnemonics ∙ Overstrikes ∙ Migration level
Individual glyphs Jot (∘) ∙ Right Shoe (⊃) ∙ Up Arrow (↑) ∙ Zilde (⍬) ∙ High minus (¯) ∙ Dot (.) ∙ Del (∇)
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