Dévai Gergely @ ELTE

Extend the While language with (limited) string support.

• The name of the new type: string
• String literals start and end with the “ character. There can be any number of any characters except newlines and ” characters. Backslach is allowed inside string literals, but it has no special meaning (unlike in real programming languages).
  • Examples: “”, “apple”, “123asdf>#&@\”
• It is possible to declare variables of type string.
• Expressions of type string are string literals and string variables.
• It is possible to assign a string typed expression to a string variable.
• There are two functions working with strings:
  • length: takes a string and returns an integer, the number of characters in the string
  • concat: takes two strings and returns a string, the concatenation of the parameters
• Attention: It is not possibe to input or output strings!

Taks:

• Extend the lexical analyser with the new type name and string literals.
• Extend the grammar rules as needed.
• Add string related type checking.
• Extend assembly code generation.
  • Hint: Do not store strings as character sequences, store only their lengths! This way the length function just returns the stored number, and concat becomes addition.