Built-In Classes

Several classes are built into the snail language. These cannot be redefined in a program.

Object

The Object class is the root of the class inheritance graph. All basic classes inherit from Object, and classes without an explicit parent inherit from Object. It is an error to redefine Object.

Methods

  • abort(): flushes all output and halts program execution with the error message “abort\n”.

  • copy(): produces a shallow copy of the object.1 This method will fail for an Array.

  • get_type(): returns a String with the name of the class of the object.

  • is_a(t): returns true if the class name, t, is in the inheritance graph of the object or false otherwise.

Array

The Array class represents a contiguous sequence of objects. Arrays have a fixed size.

Methods

  • length(): returns an Int of the fixed size of the Array.

Bool

The Bool class provides true and false. The default initialization for variables of type Bool is false (not void). It is an error to inherit from or redefine Bool.

Int

The Int class provides integers with 64 bits of precision. There are no methods specific to Int. The default initialization for variables of type Int is 0 (not void). It is an error to inherit from or redefine Int.

IO

The IO class provides several methods for performing simple input and output.

Methods

  • print_string(s): print the String, s, and flush standard output. This returns the self object. Every sequence of \t and \n is converted to a tab and newline, respectively. Note that snail stores these two characters separately, unlike most languages where these two characters are combined into an escape sequence.

  • print_int(i): print the Int, i, and flush standard output. This returns the self object.

  • read_string(): reads a string from the standard input, up to—but not including—the newline character or end of file. The newline character is consumed and discarded. If there is an error trying to read a line from standard input, the empty string is returned. Common errors include:
    • no input before the end of file
    • the read string contains the null character—with unicode/ASCII value 0)
  • read_int(): reads a single (possibly signed) integer, which may be preceded by whitespace. Any characters following the integer, up to and including the next newline, are discarded. If an error occurs, then 0 is returned. Common errors include:
    • no input found before the end of file
    • malformed input (there is no integer to read)
    • integer read in is less than \(-2^{63}\)
    • integer read in is greater than \(2^{63}-1\)

String

The String class provides strings, or sequences of characters. Note, however, that there is no character class in snail. The default initialization of a String is "" (not void). It is an error to inherit or redefine String.

Methods

  • concat(s): returns a String formed by concatenating the String s after self.

  • length(): returns the length of the string as an Int.

  • substr(start, length): returns a subsequence of the given String starting from position start and containing length characters. Character positions begin with 0. A runtime error is generated if the specified substring is out of range.

  1. A shallow copy of a copies a itself (creating new locations for each member variable), but does not recursively copy objects that a refers to. ↩

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