Scheme Pretty-Printing

Question

Scheme is an expression language. This means that everything that is entered to the Scheme interpreter/compiler is an expression. Expressions are separated by blank space (blank, tabs, new-lines). Expressions can be in several forms:
1. numbers - a sequence of digits, possibly preceded by a '+' or '-', possibly including a single '.' following at least one digit
2. strings - a sequence of characters (not including newlines) preceded and followed by ", with any included double-quote characters preceded by a '\', such as "This '\"' is a double-quote"
3. special constants - a '#' followed by any characters up to blank space
4. compound expressions - a (possibly empty) sequence of expressions surrounded by parentheses
5. identifiers - a sequence of non-blank characters not including the characters: #, ", \, (, and )

Input

A sequence of Scheme expressions.

Output

The same sequence of expressions, reformatted to make them more readable. The rules you must follow are:

1. All top level expressions will start with no leading blanks on a line.
2. A compound expression with the first sub-expression begin the identifier define is define-form. The second sub-expression will be an identifier and should go on the same line as the word define. If the third (and last) expression is compound it should start on the following line, indented 3 spaces. Otherwise, the whole define-form should be on a single line.
3. A compound expression with the first sub-expression being the identifier lambda is a lambda-form. The second sub-expression will be an identifier or compound expression and should go on the same line as the word lambda. All subsequent expressions should start on a new line, indented by an additional 3 spaces.
4. A compound expression with the first sub-expression being the identifier if is an if-form. The second sub-expression will be an identifier or compound expression and should go on the same line as the word if. All subsequent expressions should start on a new line, indented by an additional 4 spaces.
5. All other compound expressions are function applications. If any of the sub-expressions are compound, the first two sub-expressions will be on the same line and all subsequent sub-expressions will be on new lines, indented to align with the second sub-expression.
6. In all other cases, all blank space between elements of a compound expression will be replaced by a single space.

Sample Input

(define abc+ (lambda (@1 $f) (if (if
$f a b) (@1
3 4) (b (d e) (f "g")))))
(define
a 42)
(+ a (- b c))

Sample Output

(define abc+
(lambda (@1 $f)
(if (if $f
a
b)
(@1 3 4)
(b (d e)
(f "g")))))
(define a 42)
(+ a
(- b c))

Answer 1

http://blog.csdn.net/chengouxuan/article/details/6865197