(r5rs.info.gz) Lexical structure

Info Catalog

(r5rs.info.gz) Formal syntax

(r5rs.info.gz) Formal syntax

(r5rs.info.gz) External representation

 
 7.1.1 Lexical structure
 -----------------------
 
 This section describes how individual tokens (identifiers, numbers,
 etc.) are formed from sequences of characters.  The following sections
 describe how expressions and programs are formed from sequences of
 tokens.
 
 <Intertoken space> may occur on either side of any token, but not
 within a token.
 
 Tokens which require implicit termination (identifiers, numbers,
 characters, and dot) may be terminated by any <delimiter>, but not
 necessarily by anything else.
 
 The following five characters are reserved for future extensions to the
 language: [ ] { } |
 
 <token> -> <identifier> | <boolean> | <number>
      | <character> | <string>
      | ( | ) | #( | ' | ` | , | ,@ | .
 <delimiter> -> <whitespace> | ( | ) | " | ;
 <whitespace> -> <space or newline>
 <comment> -> ;  <all subsequent characters up to a
                  line break>
 <atmosphere> -> <whitespace> | <comment>
 <intertoken space> -> <atmosphere>*
 
 <identifier> -> <initial> <subsequent>*
      | <peculiar identifier>
 <initial> -> <letter> | <special initial>
 <letter> -> a | b | c | ... | z
 
 <special initial> -> ! | $ | % | & | * | / | : | < | =
      | > | ? | ^ | _ | ~
 <subsequent> -> <initial> | <digit>
      | <special subsequent>
 <digit> -> 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
 <special subsequent> -> + | - | . | @
 <peculiar identifier> -> + | - | ...
 <syntactic keyword> -> <expression keyword>
      | else | => | define
      | unquote | unquote-splicing
 <expression keyword> -> quote | lambda | if
      | set! | begin | cond | and | or | case
      | let | let* | letrec | do | delay
      | quasiquote
 
 `<variable> => <'any <identifier> that isn't
                 also a <syntactic keyword>>
 
 <boolean> -> #t | #f
 <character> -> #\ <any character>
      | #\ <character name>
 <character name> -> space | newline
 
 <string> -> " <string element>* "
 <string element> -> <any character other than " or \>
      | \" | \\
 
 <number> -> <num 2>| <num 8>
      | <num 10>| <num 16>
 
 The following rules for <num R>, <complex R>, <real R>, <ureal R>,
 <uinteger R>, and <prefix R> should be replicated for R = 2, 8, 10, and
 16.  There are no rules for <decimal 2>, <decimal 8>, and <decimal 16>,
 which means that numbers containing decimal points or exponents must be
 in decimal radix.
 
 <num R> -> <prefix R> <complex R>
 <complex R> -> <real R> | <real R> @ <real R>
     | <real R> + <ureal R> i | <real R> - <ureal R> i
     | <real R> + i | <real R> - i
     | + <ureal R> i | - <ureal R> i | + i | - i
 <real R> -> <sign> <ureal R>
 <ureal R> -> <uinteger R>
     | <uinteger R> / <uinteger R>
     | <decimal R>
 <decimal 10> -> <uinteger 10> <suffix>
     | . <digit 10>+ #* <suffix>
     | <digit 10>+ . <digit 10>* #* <suffix>
     | <digit 10>+ #+ . #* <suffix>
 <uinteger R> -> <digit R>+ #*
 <prefix R> -> <radix R> <exactness>
     | <exactness> <radix R>
 
 <suffix> -> <empty>
     | <exponent marker> <sign> <digit 10>+
 <exponent marker> -> e | s | f | d | l
 <sign> -> <empty>  | + |  -
 <exactness> -> <empty> | #i | #e
 <radix 2> -> #b
 <radix 8> -> #o
 <radix 10> -> <empty> | #d
 <radix 16> -> #x
 <digit 2> -> 0 | 1
 <digit 8> -> 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
 <digit 10> -> <digit>
 <digit 16> -> <digit 10> | a | b | c | d | e | f
 

Info Catalog

(r5rs.info.gz) Formal syntax

(r5rs.info.gz) Formal syntax

(r5rs.info.gz) External representation