Migration level
Migration level (⎕ML, ⎕EL) or Evolution level is a number that, in Dyalog APL and APL+Win respectively, determines exact where the original NARS specification and the current APL2 implementation differ. A lower value represents a behaviour closer to NARS, while a higher the value represents a behaviour closer to APL2.
Dyalog APL currently offers the following settings:
⎕ML=0
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Z←∊R
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Monadic ∊ is interpreted as type rather than enlist.
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⎕ML=1
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Default behaviour | |
⎕ML≤2
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Z←↑R
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Monadic ↑ is interpreted as first rather than mix.
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Z←⊃R
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Monadic ⊃ is interpreted as mix rather than first.
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Z←≡R
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Monadic ≡ returns a positive rather than a negative value, if its argument has non-uniform depth.
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⎕ML=3
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R←X⊂[K]Y
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Dyadic ⊂ is interpreted as partition (⊆) rather than partitioned enclose.
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⎕TC
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The order of the elements of ⎕TC is the same as in APL2.
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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
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Epsilon←{×⎕NC'⍺':⍺∊⍵ ⋄ ⊃0⍴⊂⍵}
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'''[^'']+''' '∊'⎕R'&' 'Epsilon'
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⎕ML=2
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UpArrow←{×⎕NC'⍺':⍺↑⍵ ⋄ ⊃⍵}
RightShoe←{×⎕NC'⍺':⍺↑⍵ ⋄ ↑⍵}
EqualUnderbar←|≡
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'''[^'']+''' '↑' '⊃' '≡'⎕R'&' 'UpArrow' 'RightShoe' 'EqualUnderbar'
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⎕ML=3
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UpArrow←{×⎕NC'⍺':⍺↑⍵ ⋄ ⊃⍵}
RightShoe←{×⎕NC'⍺':⍺↑⍵ ⋄ ↑⍵}
EqualUnderbar←(|≡)
LeftShoe←{×⎕NC'⍺':⍺⊆⍵ ⋄ ⊂⍵}
quadTC←(⎕UCS 8 13 10)
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'''[^'']+''' '↑' '⊃' '≡' '⊂' '⎕TC'⎕R'&' 'UpArrow' 'RightShoe' 'EqualUnderbar' 'LeftShoe' ' quadTC'
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Alternatively, the definitions can be used directly inside the text substitutions, whereby one avoids polluting existing code with these cover names.