LISP S-expressions

Textual representation

Special characters are:

• the parenthesis ( and ),
• the double quote ",
• the vertical bar |.

Symbols are represented by their name. Vertical bars | can be used to delimit names that contain blanks, special characters, non printable characters, non-ASCII characters, or can be confused as a number.

Numbers follow the syntax specified by the C function strtol() with base=0.

Strings are delimited by double quotes. All C string escapes are recognized. Non-printable ASCII characters must be escaped.

List are represented by an open parenthesis ( followed by the space separated list elements, followed by a closing parenthesis ).

When the cdr of the last pair is non zero, the closed parenthesis is preceded by a space, a dot ., a space, and the textual representation of the cdr. (This is only partially supported by Python bindings.)

Symbols

class djvu.sexpr.Symbol(str)

>>> Symbol('ham')
Symbol('ham')

S-expressions

class djvu.sexpr.Expression

Inheritance diagram:

as_string([width])

Return a string representation of the expression.

print_into(file[, width])

Print the expression into the file.

value

The actual “pythonic” value of the expression.

class djvu.sexpr.IntExpression

IntExpression can represent any integer in range \left[-2^{29}, 2^{29}\right).

To create objects of this class, use the Expression constructor:

>>> x = Expression(42)
>>> x
Expression(42)
>>> type(x)
<class 'djvu.sexpr.IntExpression'>
>>> x.as_string()
'42'
>>> x.value
42

class djvu.sexpr.ListExpression

To create objects of this class, use the Expression constructor:

>>> x = Expression([4, 2])
>>> x
Expression((4, 2))
>>> type(x)
<class 'djvu.sexpr.ListExpression'>
>>> x.as_string()
'(4 2)'
>>> x.value
(4, 2)

class djvu.sexpr.StringExpression

To create objects of this class, use the Expression constructor:

>>> x = Expression('eggs')
>>> x
Expression('eggs')
>>> type(x)
<class 'djvu.sexpr.StringExpression'>
>>> x.as_string()
'"eggs"'
>>> x.value
'eggs'

class djvu.sexpr.SymbolExpression

To create objects of this class, use the Expression constructor:

>>> x = Expression(Symbol('ham'))
>>> x
Expression(Symbol('ham'))
>>> type(x)
<class 'djvu.sexpr.SymbolExpression'>
>>> x.as_string()
'ham'
>>> x.value
Symbol('ham')

Variétés

djvu.sexpr.EMPTY_LIST

Empty list S-expression.

>>> EMPTY_LIST
Expression(())