severalwhile

Severalwhile is a hypothetical programming construct described in discussions of language design. It refers to a composite control structure that coordinates multiple while-style guards under a single enclosing construct. The idea is to express several looping conditions and their corresponding bodies as a single declarative unit, potentially easing analysis and optimization in compilers or interpreters.

Semantics: Each sub-loop has its own condition and body. On each iteration of severalwhile, the system evaluates all sub-conditions. Sub-branches whose conditions are true execute their bodies. After all sub-branches have run for that iteration, the loop can either repeat or terminate according to a global termination rule. Language discussions commonly specify an evaluation mode: sequential by default (one sub-loop after another) or parallel (sub-loops may run concurrently). Some designs also allow a global predicate that determines when the entire severalwhile construct should stop.

Syntax: A typical form is shown in pseudo-syntax, for example: severalwhile { while C1 do B1; while C2 do B2; ... } or severalwhile (C1 -> B1, C2 -> B2, ...) { ... } depending on the language. Each body may be an expression, assignment, or function call. A global termination condition can be defined to end the loop when a certain state is reached.

Example: severalwhile { while x > 0 do x--; while y < 100 do y++; } will continue until both x <= 0 and y >= 100, with behavior depending on the chosen evaluation mode.

History and usage: Severalwhile is not an established feature in any major language; it appears in theoretical discussions and experimental languages as an illustration of how multiple looping guards might be coordinated. It is used to analyze dependencies, synchronization, and potential parallel execution in loop bodies.

See also: while loop, parallel constructs, control-flow concepts.