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Gforth Manual

3.6 Stack Manipulation

Stack manipulation words rearrange the data on the stack.

1 .s drop .s 1 .s dup .s drop drop .s 1 2 .s over .s drop drop drop 1 2 .s swap .s drop drop 1 2 3 .s rot .s drop drop drop

These are the most important stack manipulation words. There are also variants that manipulate twice as many stack items:

1 2 3 4 .s 2swap .s 2drop 2drop

Two more stack manipulation words are:

1 2 .s nip .s drop 1 2 .s tuck .s 2drop drop

Assignment:

Replace nip and tuck with combinations of other stack manipulation words.

Given: How do you get: 1 2 3 3 2 1 1 2 3 1 2 3 2 1 2 3 1 2 3 3 1 2 3 1 3 3 1 2 3 2 1 3 1 2 3 4 4 3 2 1 1 2 3 1 2 3 1 2 3 1 2 3 4 1 2 3 4 1 2 1 2 3 1 2 3 1 2 3 4 1 2 3 1 3

5 dup * .

Assignment:

Write 17^3 and 17^4 in Forth, without writing 17 more than once. Write a piece of Forth code that expects two numbers on the stack (a and b, with b on top) and computes (a-b)(a+1).

Reference: 5.6 Stack Manipulation.