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Strings can be written in two ways: using double quotes (`"`), as we did above,
or using single quotes (`'`). In both types of strings, you can escape a quote
that otherwise would signify the end of the string by adding a single backslash
before it. Consequently, backslashes also have to be escaped in the same way.
The following are all valid strings:
"hello world"
'hello world'
"it's a beautiful day"
'it\'s a beautiful day'
"this is a backslash: \\"
"this is a double quote: \""
""
''
Aside from strings, there are two more types of values that you can use when
writing alv programs: numbers and booleans. Numbers use the digits 0-9 and
can be integers, contain a decimal point, or start or end with a decimal point.
Numbers can start with a negetive sign. The following are all valid numbers:
0
12
-7
0.1
10.
.1
123.
There are only two boolean values, `true` and `false`:
true
false
The operator [print][], that we have been using above, only works on strings,
but there is a similar operator called [trace][] that can be used to inspect
any kind of value. It prints the value itself alongside more information, such
as the values type. Give it a try:
(trace "hello")
(trace 2)
(trace true)
This will print the following:
```output
changes to files: values.alv
trace "hello": <str= "hello">
trace 2: <num= 2>
trace true: <bool= true>
```
On the left side of the colon, [trace][] prints the expression that it is
evaluating. On the right side, three pieces of information are shown:
- the *type*: `str`, `num`, `bool`
- the *value* itself: `"hello"`, `2`, `true`
- the *kind* of the result: `=`
`=` means that these values are *constant* - they will not change by themselves
until the code is changed. For simple values like these that seems obvious, but
in `alv` we can also create values tha change over time, as we will see soon.
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