- Symbols:
symbols atoms starting with an alphabetic character. Unlike
numbers and strings, they may be used as variables. Examples
are
a bcd f6 myfunc
plus cond
Symbols may be created from strings by using the function intern - Numbers:
In this version of scheme all numbers are doubles, there is no
distinction between floats, doubles and ints. Examples are
1
1.4
3.14
345
3456756.4345476
Numbers evaluate to themselves, that is the value of the atom 2
is the number 2. - Strings:
Strings are bounded by the double quote characters ".
For example
"a"
"abc"
"This is a string"
Strings evaluate to themselves. They may be converted to symbols
with the function intern. If they are strings of characaters
that represent numbers you can convert a string to a number with
the function parse-number. For example
(intern "abc") => abc
(parse-number "3.14") => 3.14
Although you can make symbols from numbers you should not do that. Double quotes may be specified within a string by escaping it with a
backslash. Backslashes therefore also require an escape backslash.
That is, "ab\"c" contains four characters, a, b,
" and c. "ab\\c" also contains four characters,
a, b, \ and c. And "ab\\\"c"
contains five characters a, b, \, " and
c.
- Lists or Cons
Lists start with a left parenthesis and end with a right parenthesis
with zero or more s-expression between them. For example
(a b c)
()
(b (b d) e)
((the boy) saw (the girl (in (the park))))
Lists can be made by various functions most notably cons and
list. cons returns a list whose first item is the first
item in the list, standardly called its car, and whose remainder,
standardly called its cdr, is the second argument of cons.
(cons 'a '(b c)) => (a b c)
(cons '(a b) '(c d)) => ((a b) c d)
- Functions:
Functions may be applied explicity bu the function apply
or more normally as when the appear as the first item in a list
to be evaluated. The normal way to define function is using
the define function. For example
(define (ftoc temp)
(/ (* (- temp 32) 5) 9))
This binds the function to the variable ftoc. Functions
can also be defined anonymously which sometimes is convinient.
(lambda (temp)
(/ (* (- temp 32) 5) 9))
returns a function. - Others:
other internal types are support by Festival's scheme including some
inportant object types use for synthesis such as utterances, waveforms,
items etc. The are normally printed as in the form
#<Utterance 6234>
#%lt;Wave 1294>
The rpint form is a convinience form only. Enter that string of
characters will not allow a reference to that object. The number is
unique to that object instance (it is actually the internal address of
the object), and can be used visually to note if objects are the same or
not.
