Processes a series of "assignment" expressions, applying them in reverse to the given body. else/elif and except/finally can also be given, where else/elif triggers if any "matching" assignments fail, and except/finally have the usual behavior.

An assignment expression can be one of:

• a normal assignment, of the form a := b or a = b; prepended to the body verbatim
• a matching assignment, of the form a :=? b or a =? b; prepends an assignment a := b and stops execution or jumps to else block if the assignment fails
• result assignment, of the form result a or result a := b; returns a as the value of the expression
• an iterator assignment, of the form a in b; wraps the body in for a in b: ... , allowing complex assignments for a
• a filter, of the form filter cond; wraps the body in if cond: ... statement
• a list of other assignment expressions, as in tap: a; b; c; ... do: ...; applies assignments in reverse order
• any other statement; also prepended to the block verbatim

Example:

import assigns
let val = tap(a := 5): a + 1
var s: seq[int]
tap a := 5, i in 1 .. a, filter i mod 2 != 0:
  s.add(i)
doAssert s == @[1, 3, 5]
doAssert val == 6
let x = tap(a := 5, result s := newSeq[int](a), i in 0 ..< a):
  s[i] = i + 1
doAssert x == @[1, 2, 3, 4, 5]
var s2: seq[int]
tap:
  a = 5
  i in 1 .. a
  filter i mod 2 != 0
do:
  s2.add(i)
doAssert s2 == @[1, 3, 5]