Modifies the value stored in a variable by performing a binary
shift left operation with it.
Parameters:
symbol -
A symbol object identifying a variable in the current context. The
variable must contain a numeric value.
shift -
A numeric object represeting the number of bits to shift left
the value stored in variable symbol.
Returns:
The new value of the variable.
Modifies the contents of the variable identified by
symbol by performing a binary shift left by
shift bits on the value it had previously stored.
The variable binded to symbol is expected to
contain an integer object.
