Head

Head[expr] returns the head of the expression.

Attributes[Head] := {Protected}

Simple examples

In[1]:= Head[f[x]]
Out[1]= f

In[2]:= Head[x]
Out[2]= Symbol

In[3]:= Head[{x}]
Out[3]= List

In[4]:= Head[a + b]
Out[4]= Plus

In[5]:= Head[1]
Out[5]= Integer

In[6]:= Head[1.]
Out[6]= Real

In[7]:= Head[(2)/(7)]
Out[7]= Rational

In[8]:= Head[(1)/(7)]
Out[8]= Rational

In[9]:= Head["1"]
Out[9]= String

In[10]:= Head[Head[a + b[x]]]
Out[10]= Plus