/
expression_parser.go
76 lines (67 loc) · 2.07 KB
/
expression_parser.go
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package yqlib
import (
"fmt"
"strings"
)
type ExpressionNode struct {
Operation *Operation
LHS *ExpressionNode
RHS *ExpressionNode
}
type ExpressionParserInterface interface {
ParseExpression(expression string) (*ExpressionNode, error)
}
type expressionParserImpl struct {
pathTokeniser expressionTokeniser
pathPostFixer expressionPostFixer
}
func newExpressionParser() ExpressionParserInterface {
return &expressionParserImpl{newParticipleLexer(), newExpressionPostFixer()}
}
func (p *expressionParserImpl) ParseExpression(expression string) (*ExpressionNode, error) {
log.Debug("Parsing expression: [%v]", expression)
tokens, err := p.pathTokeniser.Tokenise(expression)
if err != nil {
return nil, err
}
var Operations []*Operation
Operations, err = p.pathPostFixer.ConvertToPostfix(tokens)
if err != nil {
return nil, err
}
return p.createExpressionTree(Operations)
}
func (p *expressionParserImpl) createExpressionTree(postFixPath []*Operation) (*ExpressionNode, error) {
var stack = make([]*ExpressionNode, 0)
if len(postFixPath) == 0 {
return nil, nil
}
for _, Operation := range postFixPath {
var newNode = ExpressionNode{Operation: Operation}
log.Debugf("pathTree %v ", Operation.toString())
if Operation.OperationType.NumArgs > 0 {
numArgs := Operation.OperationType.NumArgs
if numArgs == 1 {
if len(stack) < 1 {
return nil, fmt.Errorf("'%v' expects 1 arg but received none", strings.TrimSpace(Operation.StringValue))
}
remaining, rhs := stack[:len(stack)-1], stack[len(stack)-1]
newNode.RHS = rhs
stack = remaining
} else if numArgs == 2 {
if len(stack) < 2 {
return nil, fmt.Errorf("'%v' expects 2 args but there is %v", strings.TrimSpace(Operation.StringValue), len(stack))
}
remaining, lhs, rhs := stack[:len(stack)-2], stack[len(stack)-2], stack[len(stack)-1]
newNode.LHS = lhs
newNode.RHS = rhs
stack = remaining
}
}
stack = append(stack, &newNode)
}
if len(stack) != 1 {
return nil, fmt.Errorf("bad expression, please check expression syntax")
}
return stack[0], nil
}