A wide-spectrum language (WSL) is a programming language designed to be simultaneously a low-level and a high-level language - possibly a non-executable specification language. Wide-spectrum languages are designed to support a programming methodology based on program refinement.
The concept was introduced by F. L. Bauer et al. in 1978:
...The program should then be developed step by step applying correctnesspreserving transformations.... The development processthus involves usually multiple reshapings....Since most current programming languages do not containall the concepts needed for the formulation of the differentversions, the programmer is nowadays forced touse different languages. To avoid the transition fromone language to another, it seems appropriate to haveone coherent language frame covering the whole spectrumoutlined above, i.e. a wide spectrum language.[1]
The advantage of a single language rather than separate specification, high-level, and low-level languages is that the program can be incrementally refined, with intermediate versions retaining some higher-level and some lower-level constructs.
Bauer's group developed the CIP-L wide-spectrum language and the CIP-S program transformation system.