Reap

Reap[expr]
gives the value of expr together with all expressions to which Sow has been applied during its evaluation. Expressions sown using Sow[e] or Sow[e, tag_i] with different tags are given in different lists.

Reap[expr, patt]
reaps only expressions sown with tags that match patt.

Reap[expr, {patt₁, patt₂, ...}]
puts expressions associated with each of the patt_i in a separate list.

Reap[expr, patt, f]
returns {expr, {f[tag₁, {e₁₁, e₁₂, ...}], ...}}.

MORE INFORMATION

Sow and Reap provide a convenient way to accumulate a list of intermediate results in a computation.

Reap accumulates expressions in the order in which Sow is applied to them.

Expressions sown with a particular tag are collected by the innermost Reap whose pattern matches the tag.

Reap[expr] is equivalent to Reap[expr, _].

Reap has attribute HoldFirst.

EXAMPLES

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Basic Examples (2)

Evaluate a sequence of expressions, "reaping" ones that have been "sown":

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Compute a sum, "reaping" i^2 "sown" at each step:

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Scope (1)

Generalizations & Extensions (1)

Applications (3)

Properties & Relations (3)