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Flat

Status: Partial

implemented with documented limitations or caveats; some argument forms fall through to symbolic/unevaluated output.

Description

Flat is an attribute that can be assigned to a symbol f to indicate that all expressions involving nested functions f should be flattened out. This property is accounted for in pattern matching.

Examples

No verified examples yet for this function.

Implementation notes

Flat is an attribute marker symbol, not a function. attr.c maps the name to the ATTR_FLAT bitflag (via SetAttributes/the attribute name table). When a head carries ATTR_FLAT, the evaluator's flattening step (eval_flatten_args in eval.c) splices nested same-head calls into the parent argument list, giving associative behaviour (f[a, f[b, c]] → f[a, b, c]). The pattern matcher (match.c) also consults ATTR_FLAT when matching sequence patterns against such heads. Plus and Times set this bit. The symbol Flat itself only ever appears as an argument to Attributes/SetAttributes or inside a Function[..., Flat] attribute spec (pure_function_attributes in purefunc.c maps SYM_Flat → ATTR_FLAT).

Attributes: none registered.

Implementation status

Partial — implemented with documented limitations or caveats; some argument forms fall through to symbolic/unevaluated output.

References

Notes & additional examples

Worked examples

In[1]:= SetAttributes[f, Flat]
Out[1]= Null

In[2]:= f[f[a, b], c]
Out[2]= f[a, b, c]

In[3]:= f[a, f[b, f[c, d]]]
Out[3]= f[a, b, c, d]

Notes

Flat marks a head as associative, so nested calls with the same head are flattened into a single argument sequence. Plus and Times carry this attribute by default; the flattening is also accounted for during pattern matching.