<pre class="grammar">
Production  = production_name "=" [ Expression ] "." .
Expression  = Alternative { "|" Alternative } .
Alternative = Term { Term } .
Term        = production_name | token [ "…" token ] | Group | Option | Repetition .
Group       = "(" Expression ")" .
Option      = "[" Expression "]" .
Repetition  = "{" Expression "}" .
</pre>

<p>
Productions are expressions constructed from terms and the following

Syntax      = { Production } .
Production  = production_name "=" [ Expression ] "." .
Expression  = Term { "|" Term } .
Term        = Factor { Factor } .
Factor      = production_name | token [ "…" token ] | Group | Option | Repetition .
Group       = "(" Expression ")" .
Option      = "[" Expression "]" .
Repetition  = "{" Expression "}" .
</pre>

<p>
Productions are expressions constructed from terms and the following

<h3 id="constants">Constants</h3>

<p>
Although the assembler takes its guidance from the Plan 9 assemblers,
it is a distinct program, so there are some differences.
One is in constant evaluation.
Constant expressions in the assembler are parsed using Go's operator
precedence, not the C-like precedence of the original.
Thus <code>3&amp;1&lt;&lt;2</code> is 4, not 0—it parses as <code>(3&amp;1)&lt;&lt;2</code>

To allow additional flags, set CGO_CFLAGS_ALLOW to a regular expression
matching the new flags. To disallow flags that would otherwise be allowed,
set CGO_CFLAGS_DISALLOW to a regular expression matching arguments
that must be disallowed. In both cases the regular expression must match
a full argument: to allow -mfoo=bar, use CGO_CFLAGS_ALLOW='-mfoo.*',

		}
	}
}

type astContext int

const (
	ctxProg astContext = iota
	ctxEmbedType
	ctxType
	ctxStmt
	ctxExpr
	ctxField
	ctxParam
	ctxAssign2 // assignment of a single expression to two variables
	ctxSwitch
	ctxTypeSwitch
	ctxFile
	ctxDecl
	ctxSpec
	ctxDefer
	ctxCall  // any function call other than ctxCall2
	ctxCall2 // function call whose result is assigned to two variables

		}
	}

	// Remove functions only used as expressions, so their respective
	// bridge functions are not generated.
	for name, used := range functions {
		if !used {
			delete(f.Name, name)
		}
	}
}

// rewriteName returns the expression used to rewrite a reference.
// If addPosition is true, add position info in the ident name.

		p.errorf("expected g or R0 through R15; found %s", name)
		return 0
	}
	return uint16(reg)
}

// Note: There are two changes in the expression handling here
// compared to the old yacc/C implementations. Neither has
// much practical consequence because the expressions we
// see in assembly code are simple, but for the record:
//
// 1) Evaluation uses uint64; the old one used int64.

	{"3<<(2+4)", 3 << (2 + 4), true},
	// Junk at EOF.
	{"3 x", 3, false},
	// Big number
	{"4611686018427387904", 4611686018427387904, true},
}

func TestExpr(t *testing.T) {
	p := NewParser(nil, nil, nil) // Expression evaluation uses none of these fields of the parser.
	for i, test := range exprTests {
		p.start(lex.Tokenize(test.input))
		result := int64(p.expr())
		if result != test.output {

}

// gofmtLineReplacer is used to put a gofmt-formatted string for an
// AST expression onto a single line. The lexer normally inserts a
// semicolon at each newline, so we can replace newline with semicolon.
// However, we can't do that in cases where the lexer would not insert
// a semicolon. We only have to worry about cases that can occur in an
// expression passed through gofmt, which means composite literals and

// text, stripped of any trailing end-of-line marker. The returned line may
// be empty. The end-of-line marker is one optional carriage return followed
// by one mandatory newline. In regular expression notation, it is `\r?\n`.
// The last non-empty line of input will be returned even if it has no
// newline.
func ScanLines(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {