Transaction Application Language

Transaction Application Language or TAL (originally "Tandem Application Language") is a block-structured, procedural language optimised for use on Tandem hardware. TAL resembles a cross between C and Pascal. It was the original system programming language for Tandem computers;

The design concept of TAL, a clone of Hewlett Packard's HAL and like Burroughs Algol, is (or was) intemately associated and optimized with a microprogrammed CISC assembly language instruction set. Each TAL statement could easily compile into a sequence of instructions that manipulated data on a transient floating register stack. The register stack itself floated at the crest of the program's memory allocation stack.

The language itself has the appearance of PASCAL, with BEGIN and END statements. But, in fact, it is far more like C. It does not permit indefinite levels of procedure nesting, it does not pass complex structured arguments by value, and it does not strictly type most variable references. Programming techniques are much like C using pointers to structures, occasional overlays, deliberate string handling and casts when appropriate.

Available datatypes include 8 bit, 16 bit, 32 bit and (introduced later) 64 bit slices of memory. Microcode level support was available for null terminated character strings. However, this is not commonly used.

Origionally the Tandem NonStop operating system was written in TAL. Recently it has been completely rewritten in C and TAL has been deprecated.

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.