( Symbol Primitives

Info Catalog ( Symbol Variables ( Symbols ( Symbol Props
 21.6.4 Operations Related to Symbols
 Given any Scheme value, you can determine whether it is a symbol using
 the `symbol?' primitive:
  -- Scheme Procedure: symbol? obj
  -- C Function: scm_symbol_p (obj)
      Return `#t' if OBJ is a symbol, otherwise return `#f'.
    Once you know that you have a symbol, you can obtain its name as a
 string by calling `symbol->string'.  Note that Guile differs by default
 from R5RS on the details of `symbol->string' as regards
  -- Scheme Procedure: symbol->string s
  -- C Function: scm_symbol_to_string (s)
      Return the name of symbol S as a string.  By default, Guile reads
      symbols case-sensitively, so the string returned will have the
      same case variation as the sequence of characters that caused S to
      be created.
      If Guile is set to read symbols case-insensitively (as specified by
      R5RS), and S comes into being as part of a literal expression
      ( Literal expressions (r5rs)Literal expressions.) or by a
      call to the `read' or `string-ci->symbol' procedures, Guile
      converts any alphabetic characters in the symbol's name to lower
      case before creating the symbol object, so the string returned
      here will be in lower case.
      If S was created by `string->symbol', the case of characters in
      the string returned will be the same as that in the string that was
      passed to `string->symbol', regardless of Guile's case-sensitivity
      setting at the time S was created.
      It is an error to apply mutation procedures like `string-set!' to
      strings returned by this procedure.
    Most symbols are created by writing them literally in code.  However
 it is also possible to create symbols programmatically using the
 following `string->symbol' and `string-ci->symbol' procedures:
  -- Scheme Procedure: string->symbol string
  -- C Function: scm_string_to_symbol (string)
      Return the symbol whose name is STRING.  This procedure can create
      symbols with names containing special characters or letters in the
      non-standard case, but it is usually a bad idea to create such
      symbols because in some implementations of Scheme they cannot be
      read as themselves.
  -- Scheme Procedure: string-ci->symbol str
  -- C Function: scm_string_ci_to_symbol (str)
      Return the symbol whose name is STR.  If Guile is currently
      reading symbols case-insensitively, STR is converted to lowercase
      before the returned symbol is looked up or created.
    The following examples illustrate Guile's detailed behaviour as
 regards the case-sensitivity of symbols:
      (read-enable 'case-insensitive)   ; R5RS compliant behaviour
      (symbol->string 'flying-fish)    => "flying-fish"
      (symbol->string 'Martin)         => "martin"
         (string->symbol "Malvina"))   => "Malvina"
      (eq? 'mISSISSIppi 'mississippi)  => #t
      (string->symbol "mISSISSIppi")   => mISSISSIppi
      (eq? 'bitBlt (string->symbol "bitBlt")) => #f
      (eq? 'LolliPop
        (string->symbol (symbol->string 'LolliPop))) => #t
      (string=? "K. Harper, M.D."
          (string->symbol "K. Harper, M.D."))) => #t
      (read-disable 'case-insensitive)   ; Guile default behaviour
      (symbol->string 'flying-fish)    => "flying-fish"
      (symbol->string 'Martin)         => "Martin"
         (string->symbol "Malvina"))   => "Malvina"
      (eq? 'mISSISSIppi 'mississippi)  => #f
      (string->symbol "mISSISSIppi")   => mISSISSIppi
      (eq? 'bitBlt (string->symbol "bitBlt")) => #t
      (eq? 'LolliPop
        (string->symbol (symbol->string 'LolliPop))) => #t
      (string=? "K. Harper, M.D."
          (string->symbol "K. Harper, M.D."))) => #t
    Finally, some applications, especially those that generate new Scheme
 code dynamically, need to generate symbols for use in the generated
 code.  The `gensym' primitive meets this need:
  -- Scheme Procedure: gensym [prefix]
  -- C Function: scm_gensym (prefix)
      Create a new symbol with a name constructed from a prefix and a
      counter value.  The string PREFIX can be specified as an optional
      argument.  Default prefix is ` g'.  The counter is increased by 1
      at each call.  There is no provision for resetting the counter.
    The symbols generated by `gensym' are _likely_ to be unique, since
 their names begin with a space and it is only otherwise possible to
 generate such symbols if a programmer goes out of their way to do so.
 The 1.8 release of Guile will include a way of creating symbols that
 are _guaranteed_ to be unique.
Info Catalog ( Symbol Variables ( Symbols ( Symbol Props
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