Vocabulary/fordot

>> <<   Back to: Vocabulary Thru to: Dictionary

for. noun do. body end.

Repeat for each item

Control

for_ijk. noun do. body end.

Repeat for each item, named

Control

Valid only inside an explicit definition.

---

Execute the ensuing block, or body, which starts after the next do., once for each item of the noun, which results from initial evaluation of a T-block.

   for. i. nloops do.  NB. loop nloops times
<loop body>
   end.

   for_i. 'for';'each';'word' do.  NB. loop 3 times, with i successively assuming the value of the words
<loop body>
   end.

Use (for_ijk.) instead of (for.) to give a name referencing the successive items. At each iteration…

• (ijk) takes the value of the current item, and
• (ijk_index) takes the values: (0, 1, 2, …) in turn.

(ijk) (here) is a representative pronoun whose value you can inspect (read-only) at each iteration. Substitute your own choice of name, e.g. (i), which will also generate (i_index).

If you use for. with no name, the loop will be executed once for each item of the T-block, and the actual values in the T-block noun are immaterial.

---

Common uses

1. Execute a given block 3 times

3 : 0''
for. i.3 do.
  echo 'alpha'
end.
)
alpha
alpha
alpha

When you use (for.) the statements within the block can't see the actual items of the T-block.

2. Execute a given block once for each item of a given noun, viz. (0.5 + i.3), inspecting its value in turn, also its index in the list:

3 : 0''
for_ijk. 0.5 + i.3 do.
  echo 'bravo' ; ijk ; ijk_index
end.
)
┌─────┬───┬─┐
│bravo│0.5│0│
└─────┴───┴─┘
┌─────┬───┬─┐
│bravo│1.5│1│
└─────┴───┴─┘
┌─────┬───┬─┐
│bravo│2.5│2│
└─────┴───┴─┘

Details

1. The result of the T-block, which gives the values to be repeated over, may be a noun of any rank. The loop is executed once for each item of the T-block.
2. At the end of a for_ijk. loop, the names ijk and ijk_index remain locally defined.

• If the loop was exited by break. or goto., the names simply retain their latest values.
• If the loop was exited by executing all the iterations, ijk is set to an empty list and ijk_index is set to the number of iterations that were executed.

Related Primitives

Power of Verb ([x] u^:v y)

You may use these control words inside a for-loop:

• Terminate loop (break.) …see this link for a code sample.
• Terminate Iteration (continue.)