The operator precedence appears to be incorrect while parsing expressions. I noticed this while testing PR #171.

from qiskit import qasm
ast = qasm.Qasm(data="""OPENQASM 2.0;
include "qelib1.inc";
qreg qr[1];
creg cr[1];
u1(0.2*pi+0.3*pi) qr[0]; // precedence error in parser!
measure qr[0] -> cr[0];""").parse()
print(ast.qasm())

Expected Behavior

Multiplication is expected to take precedence over addition.

Current Behavior

The abridged output is

qreg qr[1];
creg cr[1];
u1(((0.200000000000000*(3.141592653589793+0.300000000000000))*3.141592653589793)) qr[0];
measure qr[0] -> cr[0];
on the current master branch (prior to accepting PR #171, which will replace pi by a symbol)

Here addition is taking precedence.

Possible Solution

The problem is near line 955 in _qasmparser.py

Steps to Reproduce (for bugs)

Run the example program above.