Mathematica Asked on February 27, 2021
Consider the definition:
Clear[fun]
fun[a_ + b_] := fun[a] + fun[b];
fun[a+b+c]
(*fun[a] + fun[b] + fun[c]*)
This works as expected. However, if we use a BlankSequence
on "b":
Clear[fun]
fun[a_ + b__] := fun[a] + fun[b];
fun[a + b + c]
(*fun[a] + fun[b, c]*)
it seems that BlankSequence
eliminates the Plus
in "b+c" and replaces it with Sequence
.
Has anybody a good explanation for this behaviour?
a+b+c == Plus[a,b,c]
So fun[a_ + b__]
== fun[Plus[a_, b__]]
when input a + b + c
,which equals Plus[a,b,c]
, mma match b
with b,c
a + b + c /. a_ + b__ :> {a, {b}}
{a, {b, c}}
Correct answer by wuyudi on February 27, 2021
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