Clear¶

Status: Stable

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

Description¶

Clear[s1, s2, ...]

clears all OwnValues and DownValues attached to the named symbols, leaving attributes and the symbol itself intact.

Notes

Clear has attribute HoldAll; Protected symbols are skipped with a diagnostic.

Examples (4)¶

Every input below was run against the current Mathilda build and its output recorded.

Applications (4)¶

In[1]:= x = 5
Out[1]= 5

In[2]:= x + 1
Out[2]= 6

In[3]:= Clear[x]
Out[3]= Null

In[4]:= x + 1
Out[4]= 1 + x

Implementation notes¶

builtin_clear (src/core.c) iterates its arguments and, for each that is a symbol, calls symtab_clear_symbol(name) to remove that symbol's OwnValues and DownValues (its rules/assignments) while leaving the symbol itself, its attributes, and any builtin binding intact. Non-symbol arguments are ignored. Returns Null. It carries ATTR_HOLDALL so the symbols are not evaluated to their current values before being cleared.

Attributes: HoldAll, Protected.

References¶

Source: src/core.c
Specification: docs/spec/builtins/assignment-and-rules.md
Tests: tests/test_autocompile.c
Tests: tests/test_catch_throw.c
Tests: tests/test_compile_assoc.c
Tests: tests/test_cond.c

Notes & additional examples¶

Notes¶

Clear[s] removes all OwnValues and DownValues attached to s, so the symbol becomes undefined again (attributes and the symbol itself are left intact).