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=== Tradfns === | === Tradfns === | ||
In some APLs, for example [[APL*PLUS]], [[tradfn]]s that declare a left argument in the [[function header]] are always ambivalent, and the code needs to check whether a left argument was supplied by the left argument name's [[name class]]; <source lang=apl inline>0 ≠ ⎕NC 'leftArg'</source>. Other APLs, for example [[Dyalog APL]], will not allow calling such a function monadically, unless the header has curly braces around the left argument name to indicate that it is optional; <source lang=apl inline> result ← {leftArg} FnName rightArg</source>. Then too, they need to query the name class, or, unique for Dyalog APL, use a specialised ''Called Monadically'' [[I-beam]], <source lang=apl inline>900⌶⍬</source>.<ref>[[Dyalog APL]] Language Reference Guide > The I-Beam Operator > [ | In some APLs, for example [[APL*PLUS]], [[tradfn]]s that declare a left argument in the [[function header]] are always ambivalent, and the code needs to check whether a left argument was supplied by the left argument name's [[name class]]; <source lang=apl inline>0 ≠ ⎕NC 'leftArg'</source>. Other APLs, for example [[Dyalog APL]], will not allow calling such a function monadically, unless the header has curly braces around the left argument name to indicate that it is optional; <source lang=apl inline> result ← {leftArg} FnName rightArg</source>. Then too, they need to query the name class, or, unique for Dyalog APL, use a specialised ''Called Monadically'' [[I-beam]], <source lang=apl inline>900⌶⍬</source>.<ref>[[Dyalog APL]] Language Reference Guide > The I-Beam Operator > [https://help.dyalog.com/latest/#Language/I%20Beam%20Functions/Called%20Monadically.htm Called Monadically]</ref> | ||
=== Dfns === | === Dfns === | ||
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[[Dfn]]s are always ambivalent, even if they reference <source lang=apl inline>⍺</source>. (This is in contrast with [[dop]]s which have a fixed [[operator valence]] determined by the presence of an unquoted <source lang=apl inline>⍵⍵</source> in their code.) Like tradfns, the dfn can check the name class (<source lang=apl inline>0 ≠ ⎕NC '⍺'</source>). | [[Dfn]]s are always ambivalent, even if they reference <source lang=apl inline>⍺</source>. (This is in contrast with [[dop]]s which have a fixed [[operator valence]] determined by the presence of an unquoted <source lang=apl inline>⍵⍵</source> in their code.) Like tradfns, the dfn can check the name class (<source lang=apl inline>0 ≠ ⎕NC '⍺'</source>). | ||
However, most APLs that support dfns also allow a statement of the structure <source lang=apl inline>⍺ ← defaultValue</source> which skipped if the function was called dyadically.<ref>[[Dyalog APL]] Programming Reference Guide > Defined Functions & Operators > Direct Functions & Operators > [ | However, most APLs that support dfns also allow a statement of the structure <source lang=apl inline>⍺ ← defaultValue</source> which skipped if the function was called dyadically.<ref>[[Dyalog APL]] Programming Reference Guide > Defined Functions & Operators > Direct Functions & Operators > [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Default%20Left%20Argument.htm Default Left Argument]</ref> This syntax also allows assigning a function, or even an operator, to <source lang=apl inline>⍺</source>, thus streamlining many ambivalent definitions. For example, we can create a Nth root function which defaults to being the square root when used monadically: | ||
[https://tio.run/##SyzI0U2pTMzJT///Pyg/v@RR24RqLgUgeNS7C8g2grK3KmgpHN4OFOOqhahTMDQw4DJWADONzAE Try it online!] | [https://tio.run/##SyzI0U2pTMzJT///Pyg/v@RR24RqLgUgeNS7C8g2grK3KmgpHN4OFOOqhahTMDQw4DJWADONzAE Try it online!] | ||
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=== Documentation === | === Documentation === | ||
* [http://microapl.com/apl_help/ch_020_010_070.htm APLX] | * [http://microapl.com/apl_help/ch_020_010_070.htm APLX] | ||
* [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/Model%20Syntax.htm Dyalog] | * [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/TradFns/Model%20Syntax.htm Dyalog] | ||
== References == | == References == |