Rows operators (The GNU Algol 68 Compiler)

### 6.4 Rows operators ¶

The following operators work on any row mode, denoted below using the pseudo-mode `rows`.

Operator: lwb `= (rows a) int` ¶

  Monadic operator that yields the lower bound of the first bound pair of the descriptor of the value of `a`.

Operator: upb `= (rows a) int` ¶

  Monadic operator that yields the upper bound of the first bound pair of the descriptor of the value of `a`.

Operator: lwb `= (int n, rows a) int` ¶

  Dyadic operator that yields the lower bound in the n-th bound pair of the descriptor of the value of `a`, if that bound pair exists. Attempting to access a non-existing bound pair results in a run-time error.

Operator: upb `= (int n, rows a) int` ¶

  Dyadic operator that yields the upper bound in the n-th bound pair of the descriptor of the value of `a`, if that bound pair exists. Attempting to access a non-existing bound pair results in a run-time error.