5.5. LISTS AND QUASI QUOTED LISTS

71

'(+ 1 2 3)

evaluates to the list (+ 1 2 3).

Exercise 17 Create the following servlet

; thisisalist.servlet

'(string append "this" "is" "a" "list")

and see what happens when you visit this servlet with and without the initial

single quote ('). Try other S expressions with and without quotes. In fact, you

can put a quote in front of any of the previous servlets you've created and see

what happens. Try to write a simple explanation for what is going on.

Scheme lists can contain sublists and this is a convenient way of representing

a table of data, e.g.

'(

(name age sex)

(john 22

male)

(jiri 20

male)

(anzy 18

female)

(miri 17

female)

)

To make this into a table we use the  trs  procedure defined in the  tables.scm 

library. This procedure takes a list of lists (one for each row) and creates a  tr 

element for each of these lists.

5.5

Lists and Quasi quoted lists

You can also create lists using the list procedure, e.g.

(list

(list {Hello there} (+ 1 2 3 4 5))

(list {Goodbye} (* 1 2 3 4 5)))

Note that this expression evaluates to

'(("Hello there" 15) ("Goodbye" 120))

You can also have the same effect using a back quote  `  instead of a single

quote ('), and then putting a comma (,) in front of those expression you want

to be evaluated. This is called quasi quote notation. In our case, we could write

the previous example as:

`(("Hello there"

,(+ 1 2 3 4 5))

("Goodbye"

,(* 1 2 3 4 5)))