Stack Effect Diagrams
As an aid to understanding the effect of statement, a short comment is used showing the top of the stack before and after the statement. The top of the stack is rightmost if there are multiple items. This notation is commonly used in the Forth language, where comments are enclosed in parentheses.
( before -- after )For example, the basic Forth stack operators are described:
dup ( a -- a a ) drop ( a -- ) swap ( a b -- b a ) over ( a b -- a b a ) rot ( a b c -- b c a )And the fib function below is described:
fib ( n -- fib )It is equivalent to preconditions and postconditions in Hoare's logic. Both comments may also be referenced as assertions, thought not necessarily in context of Stack-based languages.
Read more about this topic: Stack-oriented Programming Language
Famous quotes containing the words stack, effect and/or diagrams:
““Farewell to barn and stack and tree,
Farewell to Severn shore.
Terence, look your last at me,
For I come home no more.”
—A.E. (Alfred Edward)
“We all have—to put it as nicely as I can—our lower centres and our higher centres. Our lower centres act: they act with terrible power that sometimes destroys us; but they don’t talk.... Since the war the lower centres have become vocal. And the effect is that of an earthquake. For they speak truths that have never been spoken before—truths that the makers of our domestic institutions have tried to ignore.”
—George Bernard Shaw (1856–1950)
“Professors could silence me then; they had figures, diagrams, maps, books.... I was learning that books and diagrams can be evil things if they deaden the mind of man and make him blind or cynical before subjection of any kind.”
—Agnes Smedley (1890–1950)