Variant: Difference between revisions
Jump to navigation
Jump to search
m (→Usage) |
m (Text replacement - "</source>" to "</syntaxhighlight>") |
||
| (One intermediate revision by the same user not shown) | |||
| Line 1: | Line 1: | ||
{{Built-ins|Variant|⍠|⎕OPT}} or '''Custom''' (<code>:</code> in [[A Dictionary of APL]]<ref>[[Ken Iverson]]. [[A Dictionary of APL]]. [https://www.jsoftware.com/papers/APLDictionary1.htm#colon Custom]. [[APL Quote Quad]], Volume 18, Number 1, 1987-09.</ref>) and '''Fit''' in [[J]], is a special [[dyadic operator]] which takes a function as its left [[operand]] and modifies its behaviour as specified by the array right operand. | {{Built-ins|Variant|⍠|⎕OPT}} or '''Custom''' (<code>:</code> in [[A Dictionary of APL]]<ref>[[Ken Iverson]]. [[A Dictionary of APL]]. [https://www.jsoftware.com/papers/APLDictionary1.htm#colon Custom]. [[APL Quote Quad]], Volume 18, Number 1, 1987-09.</ref>) and '''Fit''' in [[J]], is a special [[dyadic operator]] which takes a function as its left [[operand]] and modifies its behaviour as specified by the array right operand. | ||
Since < | Since <syntaxhighlight lang=apl inline>⍠</syntaxhighlight> was not in Dyalog's [[atomic vector]] when the feature was added, a system operator alternative was provided in form of <syntaxhighlight lang=apl inline>⎕OPT</syntaxhighlight>. | ||
== History == | == History == | ||
Variant dates back all the way to [[Iverson notation]] where a subscript was used to indicate which [[index origin]] a [[primitive]] would operate under. This system was dropped in [[APL\360]]. Instead, the [[system command]] < | Variant dates back all the way to [[Iverson notation]] where a subscript was used to indicate which [[index origin]] a [[primitive]] would operate under. This system was dropped in [[APL\360]]. Instead, the [[system command]] <syntaxhighlight lang=apl inline>)ORIGIN</syntaxhighlight> was provided for controlling the interpreter's global setting. This was then supplemented with a [[system variable]] to control the global state. Though this feature is still present in many APL systems, together with numerous other system variables for controlling other aspects of the system, for example [[comparison tolerance]], these global settings were recognised as an unfortunate design in that every programmer would be forced to set and localise every system variable that could affect the given code. Later, [[Ken Iverson]] envisioned a return to a per-invocation setting, similar to the original notation, but this time in the form of a dyadic operator that would customise [[primitive function]]s. | ||
Although [[SHARP APL]] didn't implement Iverson's idea, [[J]] did. Later [[Dyalog APL 13.0]] (2011) repurposed it as a way of providing auxiliary arguments to [[primitive function|primitive]] and [[system function]]s, and [[derived function|functions derived]] from [[primitive operator|primitive]] and [[system operator]]s, however its only current use in connection with primitives is to provide language settings for the Format Date-time [[I-beam]] (< | Although [[SHARP APL]] didn't implement Iverson's idea, [[J]] did. Later [[Dyalog APL 13.0]] (2011) repurposed it as a way of providing auxiliary arguments to [[primitive function|primitive]] and [[system function]]s, and [[derived function|functions derived]] from [[primitive operator|primitive]] and [[system operator]]s, however its only current use in connection with primitives is to provide language settings for the Format Date-time [[I-beam]] (<syntaxhighlight lang=apl inline>1200⌶</syntaxhighlight>).<ref>[[Dyalog Ltd]]. Language Reference Guide: [https://help.dyalog.com/latest/#Language/I%20Beam%20Functions/Format%20Datetime.htm Format Date-time].</ref> | ||
== Usage == | == Usage == | ||
The Dyalog system operator < | The Dyalog system operator <syntaxhighlight lang=apl inline>⎕S</syntaxhighlight> takes as operands text to be searched for, and what to return for each match (with <code>&</code> meaning the matched text): | ||
< | <syntaxhighlight lang=apl> | ||
('abra'⎕S'&')'Abrabrabra' | ('abra'⎕S'&')'Abrabrabra' | ||
abra | abra | ||
</ | </syntaxhighlight>{{Works in|[[Dyalog APL]]}} | ||
Only one match is found, because < | Only one match is found, because <syntaxhighlight lang=apl inline>⎕S</syntaxhighlight> defaults to being case sensitive and disallow overlapping matches. The variant operator can be used to enable case insensitivity: | ||
< | <syntaxhighlight lang=apl> | ||
('abra'⎕S'&'⍠1)'Abrabrabra' | ('abra'⎕S'&'⍠1)'Abrabrabra' | ||
Abra abra | Abra abra | ||
</ | </syntaxhighlight>{{Works in|[[Dyalog APL]]}} | ||
This usage with a [[simple scalar]] right operand is in line with Iverson's design: | This usage with a [[simple scalar]] right operand is in line with Iverson's design: | ||
< | <syntaxhighlight lang=j> | ||
1 = 1+1e_14 NB. equivalent to 1 = 1+1e¯14 in Dictionary APL | 1 = 1+1e_14 NB. equivalent to 1 = 1+1e¯14 in Dictionary APL | ||
1 | 1 | ||
1 (= !. 0) 1+1e_14 NB. equivalent to 1 (= : 0) 1+1e¯14 in Dictionary APL | 1 (= !. 0) 1+1e_14 NB. equivalent to 1 (= : 0) 1+1e¯14 in Dictionary APL | ||
0 | 0 | ||
</ | </syntaxhighlight>{{Works in|[[J]]}} | ||
However, Dyalog also allows a [[wikipedia:name–value pair|name–value pair]], or a vector of name–value pairs. The above example can be spelled using the < | However, Dyalog also allows a [[wikipedia:name–value pair|name–value pair]], or a vector of name–value pairs. The above example can be spelled using the <syntaxhighlight lang=apl inline>IC</syntaxhighlight> (for ''Ignore Case'') setting name: | ||
< | <syntaxhighlight lang=apl> | ||
('abra'⎕S'&'⍠'IC'1)'Abrabrabra' | ('abra'⎕S'&'⍠'IC'1)'Abrabrabra' | ||
Abra abra | Abra abra | ||
</ | </syntaxhighlight>{{Works in|[[Dyalog APL]]}} | ||
Multiple settings can either be specified with multiple applications of variant, or by using a vector of name–value pairs. Here, < | Multiple settings can either be specified with multiple applications of variant, or by using a vector of name–value pairs. Here, <syntaxhighlight lang=apl inline>OM</syntaxhighlight> (for ''Overlapping Matches'') is enabled in addition to <syntaxhighlight lang=apl inline>IC</syntaxhighlight>: | ||
< | <syntaxhighlight lang=apl> | ||
('abra'⎕S'&'⍠'IC'1⍠'OM'1)'Abrabrabra' | ('abra'⎕S'&'⍠'IC'1⍠'OM'1)'Abrabrabra' | ||
Abra abra abra | Abra abra abra | ||
('abra'⎕S'&'⍠('IC'1)('OM'1))'Abrabrabra' | ('abra'⎕S'&'⍠('IC'1)('OM'1))'Abrabrabra' | ||
Abra abra abra | Abra abra abra | ||
</ | </syntaxhighlight>{{Works in|[[Dyalog APL]]}} | ||
== External links == | == External links == | ||
| Line 45: | Line 45: | ||
=== Documentation === | === Documentation === | ||
* [https://help.dyalog.com/latest/Content/Language/Primitive%20Operators/Variant.htm Dyalog] | * [https://help.dyalog.com/latest/Content/Language/Primitive%20Operators/Variant.htm Dyalog] | ||
* [https://code.jsoftware.com/wiki/Vocabulary/bangdot J] (as < | * [https://code.jsoftware.com/wiki/Vocabulary/bangdot J] (as <syntaxhighlight lang=j inline>!.</syntaxhighlight>) | ||
== References == | == References == | ||
<references/> | <references/> | ||
{{APL built-ins}}[[Category:Primitive operators]] | {{APL built-ins}}[[Category:Primitive operators]] | ||
Latest revision as of 10:43, 11 September 2022
⍠ ⎕OPT
|
Variant (⍠, ⎕OPT) or Custom (: in A Dictionary of APL[1]) and Fit in J, is a special dyadic operator which takes a function as its left operand and modifies its behaviour as specified by the array right operand.
Since ⍠ was not in Dyalog's atomic vector when the feature was added, a system operator alternative was provided in form of ⎕OPT.
History
Variant dates back all the way to Iverson notation where a subscript was used to indicate which index origin a primitive would operate under. This system was dropped in APL\360. Instead, the system command )ORIGIN was provided for controlling the interpreter's global setting. This was then supplemented with a system variable to control the global state. Though this feature is still present in many APL systems, together with numerous other system variables for controlling other aspects of the system, for example comparison tolerance, these global settings were recognised as an unfortunate design in that every programmer would be forced to set and localise every system variable that could affect the given code. Later, Ken Iverson envisioned a return to a per-invocation setting, similar to the original notation, but this time in the form of a dyadic operator that would customise primitive functions.
Although SHARP APL didn't implement Iverson's idea, J did. Later Dyalog APL 13.0 (2011) repurposed it as a way of providing auxiliary arguments to primitive and system functions, and functions derived from primitive and system operators, however its only current use in connection with primitives is to provide language settings for the Format Date-time I-beam (1200⌶).[2]
Usage
The Dyalog system operator ⎕S takes as operands text to be searched for, and what to return for each match (with & meaning the matched text):
('abra'⎕S'&')'Abrabrabra'
abraWorks in: Dyalog APL
Only one match is found, because ⎕S defaults to being case sensitive and disallow overlapping matches. The variant operator can be used to enable case insensitivity:
('abra'⎕S'&'⍠1)'Abrabrabra'
Abra abraWorks in: Dyalog APL
This usage with a simple scalar right operand is in line with Iverson's design:
1 = 1+1e_14 NB. equivalent to 1 = 1+1e¯14 in Dictionary APL 1 1 (= !. 0) 1+1e_14 NB. equivalent to 1 (= : 0) 1+1e¯14 in Dictionary APL 0
Works in: J
However, Dyalog also allows a name–value pair, or a vector of name–value pairs. The above example can be spelled using the IC (for Ignore Case) setting name:
('abra'⎕S'&'⍠'IC'1)'Abrabrabra'
Abra abraWorks in: Dyalog APL
Multiple settings can either be specified with multiple applications of variant, or by using a vector of name–value pairs. Here, OM (for Overlapping Matches) is enabled in addition to IC:
('abra'⎕S'&'⍠'IC'1⍠'OM'1)'Abrabrabra'
Abra abra abra
('abra'⎕S'&'⍠('IC'1)('OM'1))'Abrabrabra'
Abra abra abraWorks in: Dyalog APL
External links
Tutorials
Documentation
References
- ↑ Ken Iverson. A Dictionary of APL. Custom. APL Quote Quad, Volume 18, Number 1, 1987-09.
- ↑ Dyalog Ltd. Language Reference Guide: Format Date-time.