Strings
A string in Shen begins with " and ends with ". The basic functions for strings are 'cn' - which concatenates
two strings together, 'pos', which takes a non-negative number N (starting from zero) and returns the Nth unit
string of the string and 'tlstr' which returns all of the string apart from its leading unit string. The function
'str' places an atom into a string (effectively enclosing it in quotes).
The action of 'str' within the domain of atoms is as follows (^ is the concatenation sign).
For a symbol S, 'str' returns the string "^S^" that results from enclosing it in quotes.
In earlier versions of Shendoc (< 6.1) the question of the print representation of streams and closures was
not determined. In fact these objects are sent to 'str' in the course of printing and hence the print representation
of streams and closures depends directly on their string representation under 'str'. In point of fact it is
frequently impossible to recover the original expression that evaluated to the stream/closure and so generally
their print representation is not readable. In these cases 'str' should use the platform representation unless
this is totally confusing.
For a number N, 'str' returns a string "^M^" whose contents M are such that (= M N) is true in Shen. 'str' applied
to a large floating point number may return a string whose contents are in e number notation.
For a string S, 'str' returns a string that when printed off reads as "^S^". However the internal representation
of the string may and probably will differ from its print representation.
For the failure object, 'str' returns "..."
'str' is not defined for non-atoms. A more general function 'make-string' will place any Shen object into a string, preserving the appearance in a
way that makes it conformant to Shen printing conventions (see printing). 'string?' recognises all and only strings.
The $ notation as in ($ hello) is read in by the reader by exploding its argument. ($ hello) is read in as
"h" "e" "l" "l" "o"; this was introduced as a convenient shorthand for writing string handling programs.
Shen uses decimal notation for reading bytes and for character codes. The character string "c#67;" will be
printed as "C". Note values for n > 127 in 'c#n;" may not be supported by the platform, but the ASCII set (0-127)
should be supported.
The function 'n->string' (e.g. '(n->string 45)') maps a code point to the corresponding unit string. The
function 'string->n' is the converse. Note values for n > 127 may not be supported by the platform, but the ASCII
set (0-127) should be supported.
'intern' maps a string "^S^" to a pseudo-symbol S which may or may not be a symbol. For instance
'(intern "true")' returns 'true' which is a boolean; '(intern "123;")' returns '123;' which is not a symbol.
Note that where S is a symbol, 'intern' will return a symbol. |
