S-Lang is a powerful interpreted language that may be embedded into an application to make the application extensible. This enables the application to be used in ways not envisioned by the programmer, thus providing the application with much more flexibility and power. Examples of applications that take advantage of the interpreter in this way include the jed editor and the slrn newsreader.
The language features both global and local variables, branching and looping constructs, user-defined functions, structures, datatypes, and arrays. In addition, there is limited support for pointer types. The concise array syntax rivals that of commercial array-based numerical computing environments.
The language provides built-in support for string, integer (signed
and unsigned long and short), double precision floating point, and
double precision complex numbers. In addition, it supports user
defined structure types, multi-dimensional array types, and
associative arrays. To facilitate the construction of
sophisticated data structures such as linked lists and trees, a
`reference' type was added to the language. The reference type
provides much of the same flexibility as pointers in other
languages. Finally, applications embedding the interpreter may
also provide special application specific types, such as the
Mark_Type that the jed editor provides.
The language provides standard arithmetic operations such as
addition, subtraction, multiplication, and division. It also
provides support for modulo arithmetic as well as operations at
the bit level, e.g., exclusive-or. Any binary or unary operator
may be extended to work with any data type. For example, the
addition operator (+) has been extended to work between
string types to permit string concatenation.
The binary and unary operators work transparently with array types.
For example, if a and b are arrays, then a + b
produces an array whose elements are the result of element by
element addition of a and b. This permits one to do
vector operations without explicitly looping over the array
indices.
The S-Lang language supports several types of looping constructs and
conditional statements. The looping constructs include while,
do...while, for, forever, loop, foreach,
and _for. The conditional statements include if,
if-then-else, and !if.
User defined functions may be defined to return zero, one, or more values. Functions that return zero values are similar to `procedures' in languages such as PASCAL. The local variables of a function are always created on a stack allowing one to create recursive functions. Parameters to a function are always passed by value and never by reference. However, the language supports a reference data type that allows one to simulate pass by reference.
Unlike many interpreted languages, S-Lang allows functions to be dynamically loaded (function autoloading). It also provides constructs specifically designed for error handling and recovery as well as debugging aids (e.g., function tracebacks).
Functions and variables may be declared as private belonging to a namespace associated with the compilation unit that defines the function or variable. The ideas behind the namespace implementation stems from the C language and should be quite familiar to any one familiar with C.
The S-Lang language defines a construct called an error-block that may be used for error handling and recovery. When a non-fatal run-time error is encountered, any error blocks that have been defined are executed as the run-time stack unwinds. An error block can optionally clear the error and the program will continue running after the statement that triggered the error. This mechanism is somewhat similar to try-catch in C++.
Functions that compose the S-Lang run-time library are called
intrinsics. Examples of S-Lang intrinsic functions available
to every S-Lang application include string manipulation functions
such as strcat, strchop, and strcmp. The S-Lang
library also provides mathematical functions such as sin,
cos, and tan; however, not all applications enable the
use of these intrinsics. For example, to conserve memory, the 16
bit version of the jed editor does not provide support for any
mathematics other than simple integer arithmetic, whereas other
versions of the editor do support these functions.
Most applications embedding the languages will also provide a set of application specific intrinsic functions. For example, the jed editor adds over 100 application specific intrinsic functions to the language. Consult your application specific documentation to see what additional intrinsics are supported.
The language supports C-like stdio input/output functions such as
fopen, fgets, fputs, and fclose. In
addition it provides two functions, message and error,
for writing to the standard output device and standard error.
Specific applications may provide other I/O mechanisms, e.g.,
the jed editor supports I/O to files via the editor's
buffers.
Comprehensive information about the library may be obtained via the
World Wide Web from http://www.s-lang.org.
S-Lang as well as some programs that embed it are freely available via anonymous ftp in the United States from
It is also available outside the United States from the following mirror sites:The Usenet newsgroup alt.lang.s-lang was created for S-Lang
programmers to exchange information and share macros for the various
programs the embed the language. The newsgroup comp.editors
can be a useful resource for S-Lang macros for the jed editor.
Similarly, slrn users will find news.software.readers to be a
valuable source of information.
Finally, two mailing lists dealing with the S-Lang library have been created:
slang-announce@babayaga.math.fu-berlin.deslang-workers@babayaga.math.fu-berlin.deslang-announce-subscribe@babayaga.math.fu-berlin.de and include
the word subscribe in the body of the message. To subscribe to
the developers list, use the address
slang-workers-subscribe@babayaga.math.fu-berlin.de.