Name Rascal/Expressions/Values/String

Synopsis String values.

Syntax "StringChar1StringChar2..." where StringChar may be one of the following:

• Ordinary character: Any character except <, >, ", ' or \.
• Escaped character: Backslash \ followed by any of <, >, ", ' or \ represents the escaped character itself. Other escape sequences that are supported are:
  • \n: newline
  • \t: tab
  • \r: carriage return
  • \b: backspace
  • \f: vertical feed
  • \uhexDigit1hexDigit2hexDigit3hexDigit4 : hexadecimal escapes with four digit indexes into UNICODE.
  • \UhexDigit1hexDigit2hexDigit3hexDigit4hexDigit5hexDigit6 : hexadecimal escapes with six digit indexes into UNICODE.
  • \ahexDigit1hexDigit2: hexadecimal escapes with 2 digit indexes into ASCII (0x0 ... 0x7F).

• String Interpolation:
  
  

  Form	Description
  <Exp>	Interpolate the value of the expression as a string
  <if(Exp){> ... StringChars ... <}>	Conditional inclusion of Text, where StringChars may use variables introduced in Exp
  <if(Exp){> ... StringChars1 ... <} else {> ... StringChars2 ... <}>	Conditional inclusion of either StringChars1 or StringChars2
  <for(Exp){>... StringChars ... <}>	Iterative splicing of StringChars into the result, where StringChars may use variables introduced in Exp.
  <while(Exp){> ... StringChars ... <}>	Iterative splicing of StringChars into the result, where StringChars may use variables introduced in Exp.
  <do {>... StringChars ... <} while (Exp)>	Iterative splicing of StringChars into the result, where StringChars may use variables introduced in Exp.

• Multiline:

  Form	Description
  StringChars1\n StringChars2	Strings can be multi-line without an escape or continuation marker
  StringChars2\n ' StringChars2	A margin character ' indicates where the next line starts

Types str

Usage import String; (included in Prelude)

Details Concatenation Equal GreaterThan GreaterThanOrEqual LessThan LessThanOrEqual NotEqual Slice Subscription

Description The string values are represented by the type str and consist of character sequences surrounded by double quotes, e.g., "a" or "a\nlong\nstring".

Multiline: Strings may span more than one line. The margin character ' indicates which part of a line will be ignored. This is useful for indenting a multi-line string with the source code that generates it.

Interpolation: String literals support so-called string interpolation: inside string constants text between angle brackets (< and >) is first executed and then replaced by its string value. Various statements (if, for, while, do) also return a value and can be used in this way. In the interpolation variant of these statements the block or blocks that are part of the statement become arbitrary text (that may itself contain interpolations).

Auto-indent: Expressions that get interpolated in a string will be auto-indented. This means that each line that results from the evaluation of the expression is prefixed with the indentation level of the position of the expression in the current string.

The following functions are provided for strings:

• Concatenation: Concatenate two strings.
• Equal: Equality operator on string values.
• GreaterThan: Greater than operator on string values.
• GreaterThanOrEqual: Greater than or equal operator on string values.
• LessThan: Less than operator on string values.
• LessThanOrEqual: Less than or equal operator on string values.
• NotEqual: Not equal operator on string values.
• Slice: Retrieve a slice of a string.
• Subscription: Retrieve a substring via its index.

Examples

rascal>N = 13;
int: 13
rascal>"The value of N is <N>";
str: "The value of N is 13"
rascal>"The value of N*N is <N*N>";
str: "The value of N*N is 169"
rascal>"The value is <(N < 10) ? 10 : N*N>";
str: "The value is 169"

As you can see the string value of variables and expressions is interpolated in the result as expected.
Some examples of more advances string interpolation

rascal>"N is <if(N < 10){> small <} else {> large <}>";
str: "N is  large "
rascal>"N is <if(N < 10){> small <} else {> large (<N>)<}>";
str: "N is  large (13)"
rascal>"before <for(x<-[1..5]){>a <x> b <}>after";
str: "before a 1 b a 2 b a 3 b a 4 b after"

multi-line string

rascal>import IO;
ok
rascal>println("hello
>>>>>>>this
>>>>>>>  is
>>>>>>>    new")
hello
this
  is
    new
ok

multi-line string with margin:

rascal>if (true)
>>>>>>>  println("this is
>>>>>>>          'what
>>>>>>>          '  margins
>>>>>>>          'are good for
>>>>>>>          ");
this is
what
  margins
are good for

ok

auto indent:

rascal>str genMethod(str n) = "int <n>() {
>>>>>>>                       '  return 0;
>>>>>>>                       '}";
str (str): str genMethod(str);
rascal>str genClass() = "class myClass {
>>>>>>>                 '  <genMethod("myMethod")>
>>>>>>>                 '}";
str (): str genClass();
rascal>println(genClass());
class myClass {
  int myMethod() {
    return 0;
  }
}
ok

Benefits String interpolation enables very flexible template-based text generation as used in generators for source code, markup and the like.

[Edit] | [New Subconcept] | [Recompile Course] | [Warnings]