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FullForm

Status: Stable

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

Description

FullForm[expr]

prints expr as its raw internal tree (heads written before arguments in functional form, no operator or infix sugar).

Notes FullForm is a wrapper recognised by Print/Out; when an input evaluates to FullForm\[expr\] the wrapper is consumed by the printer and does not appear in the output.

Examples (5)

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

Applications (5)

In[1]:= FullForm[a + b]
Out[1]= Plus[a, b]

In[2]:= FullForm[1/2]
Out[2]= Rational[1, 2]

In[3]:= FullForm[x^2 + 1]
Out[3]= Plus[1, Power[x, 2]]

In[4]:= FullForm[a/b]
Out[4]= Times[a, Power[b, -1]]

In[5]:= FullForm[x_Integer /; x > 0]
Out[5]= Condition[Pattern[x, Blank[Integer]], Greater[x, 0]]

Implementation notes

FullForm is an unevaluated display wrapper: the builtin builtin_fullform (src/print.c) returns NULL, leaving FullForm[expr] intact. Rendering is done by the printer — print_standard detects the FullForm head and calls expr_print_fullform, which writes the raw tree as head[arg, ...] with no infix/operator sugar. ToString[expr, FullForm] reuses the same path via expr_to_string_fullform.

Attributes: Protected.

References

Notes & additional examples

Notes

FullForm reveals the raw internal tree, with every head written before its arguments and no special-cased syntax. It is the quickest way to see how surface notation like +, /, and ^ maps onto the underlying Plus/Rational/Power heads. Division is Times with a Power[_, -1] factor, so a/b is Times[a, Power[b, -1]]. It also exposes the desugaring of pattern syntax — x_Integer /; x > 0 is really Condition[Pattern[x, Blank[Integer]], Greater[x, 0]] — which is invaluable when debugging why a rule does or does not match.