Method parseBinaryOps

hclsyntax/parser.go:546–616

parseBinaryOps calls itself recursively to work through all of the operator precedence groups, and then eventually calls parseExpressionTerm for each operand.

(ops []map[TokenType]*Operation)

// operator precedence groups, and then eventually calls parseExpressionTerm
// for each operand.
func (p *parser) parseBinaryOps(ops []map[TokenType]*Operation) (Expression, hcl.Diagnostics) {
	if len(ops) == 0 {
		// We've run out of operators, so now we'll just try to parse a term.
		return p.parseExpressionWithTraversals()
	}

	thisLevel := ops[0]
	remaining := ops[1:]

	var lhs, rhs Expression
	var operation *Operation
	var diags hcl.Diagnostics

	// Parse a term that might be the first operand of a binary
	// operation or it might just be a standalone term.
	// We won't know until we've parsed it and can look ahead
	// to see if there's an operator token for this level.
	lhs, lhsDiags := p.parseBinaryOps(remaining)
	diags = append(diags, lhsDiags...)
	if p.recovery && lhsDiags.HasErrors() {
		return lhs, diags
	}

	// We'll keep eating up operators until we run out, so that operators
	// with the same precedence will combine in a left-associative manner:
	// a+b+c => (a+b)+c, not a+(b+c)
	//
	// Should we later want to have right-associative operators, a way
	// to achieve that would be to call back up to ParseExpression here
	// instead of iteratively parsing only the remaining operators.
	for {
		next := p.Peek()
		var newOp *Operation
		var ok bool
		if newOp, ok = thisLevel[next.Type]; !ok {
			break
		}

		// Are we extending an expression started on the previous iteration?
		if operation != nil {
			lhs = &BinaryOpExpr{
				LHS: lhs,
				Op:  operation,
				RHS: rhs,

				SrcRange: hcl.RangeBetween(lhs.Range(), rhs.Range()),
			}
		}

		operation = newOp
		p.Read() // eat operator token
		var rhsDiags hcl.Diagnostics
		rhs, rhsDiags = p.parseBinaryOps(remaining)
		diags = append(diags, rhsDiags...)
		if p.recovery && rhsDiags.HasErrors() {
			return lhs, diags
		}
	}