layout: post
title: String literals
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7 November 2011

there are many possible choices here, the wikipedia article on strings explains the many notations for a string literal ; here documents – multiple line strings explains more about strings that span multiple lines;

Perl achieves a great degree of expressiveness at the cost of introducing multiple kinds of string literals.
Perl has

• Quoted string constants
• Literal string constants
• HERE documents
• Barewords count as string constants
• Quote operator

I guess it is a bit complicated to memorize so many notations, especially if one is new to programming.

Requirements for string literals

There are therefore the following requirements for a string notation.

• One notation for string constants.
• it should not require any escape sequences, escape sequences are a bit hard to
• a string literal must express multiple line strings, sort of like “Here documents”
• must allow for embedding of code into the string; the result of evaluating the code will be inserted
  into the string.

Escape sequences can be avoided, if the definition of the HERE document contains a definition of the end of string delimiter;

String literals for the Pooh language.
A string constant can start with a single ’ characters, and must end with the same character.

‘this is a string’

‘this is a string
that spans two lines’

Or it can start with multiple ’ characters, and must end with the same number of characters.

‘’this is a string too, now I can have a single ’ character in the text of the string’’

Also one can have an expression embedded in the string

‘value of factorial of 10 is [ fact( 10 ) ] a big number’

Here the text within the brackets [ ] is computed, the result of this computation is inserted into the string.

Now if we have multiple ’ characters for start of string delimiter, then we have multiple brackets as start of expression delimiter.

‘’value of factorial of 10 is [[ fact( 10 ) ]] a big number’’

Empty string

This construct is powerful but a bit ambiguous; How do you do an empty string?
Now we can introduce the " – which will be an empty string.
Or you can call a library function emptystring() which returns an empty string.

Requirements for println function

Often one wants to print a text string followed by a new line; in Perl one does not need a separate println function – it is easy to express a string constant that has a newline at the end; in Pascal one does not have escape sequences, therefore they added the println function that writes a newline.

Also you can have a libraryfunction newline(), which returns a single newline character;