| BLISS | |
| Paradigm: | Structured, imperative (procedural) |
| Designer: | W. A. Wulf, D. B. Russell, A. N. Habermann |
| Developer: | Carnegie Mellon University |
| Latest Release Version: | BLISS-64 |
| Typing: | Typeless |
| Scope: | Lexical |
| Dialects: | Common BLISS |
| Platform: | PDP-10, PDP-11, VAX, PRISM, MIPS, DEC Alpha, IA-32, IA-64, x86-64 |
| Operating System: | Cross-platform |
| Influenced By: | ALGOL |
BLISS is a system programming language developed at Carnegie Mellon University (CMU) by W. A. Wulf, D. B. Russell, and A. N. Habermann around 1970. It was perhaps the best known system language until C debuted a few years later. Since then, C became popular and common, and BLISS faded into obscurity. When C was in its infancy, a few projects within Bell Labs debated the merits of BLISS vs. C.
BLISS is a typeless block-structured programming language based on expressions rather than statements, and includes constructs for exception handling, coroutines, and macros. It does not include a goto statement.
The name is variously said to be short for Basic Language for Implementation of System Software or System Software Implementation Language, Backwards. However, in his 2015 oral history for the Babbage Institute's Computer Security History Project, Wulf claimed that the acronym was originally based on the name "Bill's Language for Implementing System Software."[1]
The original Carnegie Mellon compiler was notable for its extensive use of optimizations, and formed the basis of the classic book The Design of an Optimizing Compiler.
Digital Equipment Corporation (DEC) developed and maintained BLISS compilers for the PDP-10,[2] PDP-11,[2] VAX,[2] DEC PRISM,[3] MIPS,[2] DEC Alpha,[2] and Intel IA-32,[2] The language did not become popular among customers and few had the compiler,[4] but DEC used it heavily in-house into the 1980s; most of the utility programs for the OpenVMS operating system were written in BLISS-32. The DEC BLISS compiler has been ported to the IA-64 and x86-64 architectures as part of the ports of OpenVMS to these platforms.[2] [5] The x86-64 BLISS compiler uses LLVM as its backend code generator, replacing the proprietary GEM backend used for Alpha and IA-64.
The BLISS language has the following characteristics:
Z+8 refers to adding 8 to the address of Z, not to its value. If one needs to add 8 to the value of Z, one must prefix the variable with a period; so one would type .Z+8 to perform this function, which adds 8 to the contents of Z.= symbol, e.g. Z=8 - which says to create a full-word constant containing 8, and store it in the location whose address corresponds to that of Z. So Z+12=14 (or, alternatively 12+Z=14) places the constant 14 into the location which is 12 words after the address of Z. (This is considered bad practice.)BEGIN statement and terminated with END. As with ALGOL, statements are separated with the semicolon (";"). When a value is computed, it is saved until the next statement terminator - which means that a value can be computed, assigned to a variable, and carried forward to the next statement, if desired. Alternatively, an open parenthesis may be used to begin a block, with the close parenthesis used to close the block. When parentheses are included in an expression, the standard precedence rules are used, in which parenthesized expressions are computed first,IF expression, which tests a true-false condition, performs alternative actions, and returns a result.EQL for equality (as opposed to overloading the = symbol for the same purpose), GTR for Greater Than, and NEQ for not equal. For example, the following code will assign the absolute value of Z to the address indicated by Q:Q = (IF .Z GTR 0 THEN .Z ELSE -.Z);
OWN keyword. Declaring a variable normally causes the compiler to allocate space for it; when necessary, a variable may be assigned a fixed machine address via the BIND declaration. This feature is primarily used for accessing either machine registers or certain special addresses.ROUTINE.MACRO.VECTOR.CASE expressionINCR expression, which is similar to ALGOL's FOR statementThe following example is taken verbatim from the Bliss Language Manual: