Slot¶

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description¶

# or Slot[n] represents the n-th argument of a pure function.

Examples¶

No verified examples yet for this function.

Implementation notes¶

Slot[n] (#, #n) is an inert marker — builtin_slot always returns NULL so the node stays unevaluated on its own. Substitution happens only when a pure Function is applied: substitute_slots walks the function body and replaces each Slot[n] with a copy of the n-th argument (when 1 ≤ n ≤ arg_count), stopping recursion at any nested Function so inner pure functions are not captured by the outer slots. ATTR_PROTECTED.

Attributes: Protected.

Implementation status¶

Stable — documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

References¶

Source: src/purefunc.c
Specification: docs/spec/builtins/functional-programming.md

Notes & additional examples¶

Worked examples¶

In[1]:= (#1 + #2 &)[3, 4]
Out[1]= 7

In[2]:= Map[#^2 &, {1, 2, 3, 4}]
Out[2]= {1, 4, 9, 16}

In[3]:= FullForm[#2]
Out[3]= Slot[2]

Notes¶

# (or #1) is Slot[1], the first argument of the enclosing pure function (&); #n refers to the n-th argument. A bare # inside Map (Out[2]) receives each list element in turn.