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Array notation: Difference between revisions
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The eventual choice was to go with existing symbols, and this had important implications for the specifics of the notation. While ideally, a notation would have been introduced for a collection of major cells, thereby handling both vectors and higher-rank arrays, a problem presents itself with [[axis|axes]] of length 1, because both square brackets and round parentheses already have meaning with when surrounding a single statement (namely [[function axis]]/[[bracket indexing]] and [[precedence]]/[[function train]]s). Thus, while <source lang=apl inline>2 ⟦3⟧</source> could have denoted the [[nested array]] <source lang=apl inline>2 (1⍴3)</source>, this isn't viable with <source lang=apl inline>2 [1⍴3]</source> because this already denotes indexing <source lang=apl inline>2</source> using the indices <source lang=apl inline>1⍴3</source>. To disambiguate, at least one statement separator or line break must be present in each level of array notation brackets and parentheses. | The eventual choice was to go with existing symbols, and this had important implications for the specifics of the notation. While ideally, a notation would have been introduced for a collection of major cells, thereby handling both vectors and higher-rank arrays, a problem presents itself with [[axis|axes]] of length 1, because both square brackets and round parentheses already have meaning with when surrounding a single statement (namely [[function axis]]/[[bracket indexing]] and [[precedence]]/[[function train]]s). Thus, while <source lang=apl inline>2 ⟦3⟧</source> could have denoted the [[nested array]] <source lang=apl inline>2 (1⍴3)</source>, this isn't viable with <source lang=apl inline>2 [1⍴3]</source> because this already denotes indexing <source lang=apl inline>2</source> using the indices <source lang=apl inline>1⍴3</source>. To disambiguate, at least one statement separator or line break must be present in each level of array notation brackets and parentheses. | ||
=== Disambiguating square brackets === | |||
The overloading of square brackets, currently in use only for [[function axis]] and [[bracket indexing]], to mean a higher-rank array, poses a problem of disambiguation in the case where there is only one major cell. For example <source lang=apl inline>'abc'[3 3]</source> could be equivalent to <source lang=apl inline>'cc'</source> or <source lang=apl inline>'abc'(1 2⍴3)</source> depending on whether the brackets are interpreted as indexing or an array. Two proposals have been made, and it is possible to support either or both: | |||
# Square brackets are interpreted as representing an array if no other interpretation is possible, e.g. immediately following an opening round parenthesis, curly brace, or square bracket, or beginning a statement. | |||
# Square brackets are interpreted as representing an array if they are "broken", i.e. contain a diamond or newline that isn't enclosed in another round parenthesis, curly brace, or square bracket. | |||
The design used in this article, which corresponds to the design proposed by [[Dyalog Ltd]], uses only the first option. | |||
=== Minimum rank of major cells === | === Minimum rank of major cells === | ||