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, lists, and
associative arrays. To facilitate the construction of
sophisticated data structures such as linked lists and trees, the
language also inclues a ``reference'' type. 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, including user-defined types.
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 stem from the C language and should be quite familiar to any one familiar with C.
The S-Lang language has a try/throw/catch/finally exception model
whose semantics are similar to that of other languages. Users may
also extend the exception class hierarchy with user-defined
exceptions. The ERROR_BLOCK based exception model of S-Lang
1.x is still supported but deprecated.
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.
Operating systems that support dynamic linking allow a slang interpreter to dynamically link additional libraries of intrinsic functions and variables into the interpreter. Such loadable objects are called modules. A separate chapter of this manual is devoted to this important feature.
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.jedsoft.org/slang/. In particular see http://www.jedsoft.org/slang/download.html for downloading the latest version of the library.
Users with generic questions about the interpreter are encouraged to
post questions to the Usenet newsgroup alt.lang.s-lang. More
specific questions relating to the use of S-Lang within some
application may be better answered in an application-specifc forum.
For example, users with questions about using S-Lang as embedded in
the jed editor are more likely to be answered in the
comp.editors newsgroup or on the jed mailing list. Similarly
users with questions concerning slrn will find
news.software.readers to be a valuable source of information.
Developers who have embedded the interpreter are encouraged to join the S-Lang mailing list. To subscribe to the list or just browse the archives, visit http://www.jedsoft.org/slang/mailinglists.html.