A single character in quotes, such as
'a', creates a scalar character rather than a string. To create a singleton string the ravel function is typically used, as in
,'a'. Ravelling a quoted literal always produces a string. This consideration only applies to exactly one character (or two quotes representing a single character, as described in the next paragraph); quotes with no characters between them (
'') form an empty string.
APL's string notation is very simple and includes only one escape: two adjacent single quotes within a string stand for one single quote character rather than ending the string and starting a new one. To strand strings together, put spaces between them. A newline character within a string produces an error. To produce newlines or other non-printing characters which would be inconvenient to include in the source, use an alternative character creation mechanism, such as Unicode Convert (
Some users of nested APLs have proposed a dedicated string datatype to allow strings to be manipulated as a single entity, and in particular, to allow them to be compared with scalar functions. In flat APLs these problems are not felt so strongly because boxed arrays behave more like a simple datatype.
|APL features |
|Built-ins||Primitives (functions, operators) ∙ Quad name|
|Array model||Shape ∙ Rank ∙ Depth ∙ Bound ∙ Index (Indexing) ∙ Axis ∙ Ravel ∙ Ravel order ∙ Element ∙ Scalar ∙ Vector ∙ Matrix ∙ Simple scalar ∙ Simple array ∙ Nested array ∙ Cell ∙ Major cell ∙ Subarray ∙ Empty array ∙ Prototype|
|Data types||Number (Boolean, Complex number) ∙ Character (String) ∙ Box ∙ Namespace ∙ Function array|
|Concepts and paradigms||Conformability (Scalar extension, Leading axis agreement) ∙ Scalar function (Pervasion) ∙ Identity element ∙ Complex floor ∙ Total array ordering ∙ Tacit programming (Function composition, Close composition) ∙ Glyph|
|Errors||LIMIT ERROR ∙ RANK ERROR ∙ SYNTAX ERROR ∙ DOMAIN ERROR ∙ LENGTH ERROR ∙ INDEX ERROR ∙ VALUE ERROR|