Control structures (original) (raw)
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Control Structures
Control words are used in
Explicit Definition (:) and are punctuation that determine the sequence of execution. Matching control words and the enclosed sentences make up a control structure. The following control words and structures are available:
assert. T
for. T do. B end. for_xyz. T do. B end.
goto_name. label_name.
if. T do. B end.
if. T do. B else. B1 end.
if. T do. B elseif. T1 do. B1 elseif. T2 do. B2 end.
select. T case. T0 do. B0 fcase. T1 do. B1 case. T2 do. B2 end.
try. B catch. B1 catchd. B2 catcht. B3 end.
while. T do. B end. whilst. T do. B end.
Words beginning with B or T denote blocks, comprising zero or more simple sentences and control structures. The last sentence executed in a T block is tested for a non-zero value in its leading atom, and determines the block to be executed next. (An empty T block result or an omitted T block tests true.) The final result is the result of the last sentence executed that was not in a T block, and if there is no such last executed sentence, the final result is i.0 0 .
These control words and control structures are further detailed in the immediately following pages.