yq/pkg/yqlib/expression_parser.go

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package yqlib
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import (
"fmt"
"strings"
)
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var myPathTokeniser = newExpressionTokeniser()
var myPathPostfixer = newExpressionPostFixer()
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type ExpressionNode struct {
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Operation *Operation
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Lhs *ExpressionNode
Rhs *ExpressionNode
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}
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type ExpressionParser interface {
ParseExpression(expression string) (*ExpressionNode, error)
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}
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type expressionParserImpl struct {
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}
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func NewExpressionParser() ExpressionParser {
return &expressionParserImpl{}
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}
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func (p *expressionParserImpl) ParseExpression(expression string) (*ExpressionNode, error) {
tokens, err := myPathTokeniser.Tokenise(expression)
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if err != nil {
return nil, err
}
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var Operations []*Operation
Operations, err = myPathPostfixer.ConvertToPostfix(tokens)
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if err != nil {
return nil, err
}
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return p.createExpressionTree(Operations)
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}
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func (p *expressionParserImpl) createExpressionTree(postFixPath []*Operation) (*ExpressionNode, error) {
var stack = make([]*ExpressionNode, 0)
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if len(postFixPath) == 0 {
return nil, nil
}
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for _, Operation := range postFixPath {
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var newNode = ExpressionNode{Operation: Operation}
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log.Debugf("pathTree %v ", Operation.toString())
if Operation.OperationType.NumArgs > 0 {
numArgs := Operation.OperationType.NumArgs
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if numArgs == 1 {
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if len(stack) < 1 {
return nil, fmt.Errorf("'%v' expects 1 arg but received none", strings.TrimSpace(Operation.StringValue))
}
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remaining, rhs := stack[:len(stack)-1], stack[len(stack)-1]
newNode.Rhs = rhs
stack = remaining
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} else if numArgs == 2 {
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if len(stack) < 2 {
return nil, fmt.Errorf("'%v' expects 2 args but there is %v", strings.TrimSpace(Operation.StringValue), len(stack))
}
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remaining, lhs, rhs := stack[:len(stack)-2], stack[len(stack)-2], stack[len(stack)-1]
newNode.Lhs = lhs
newNode.Rhs = rhs
stack = remaining
}
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}
stack = append(stack, &newNode)
}
if len(stack) != 1 {
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return nil, fmt.Errorf("expected end of expression but found '%v', please check expression syntax", strings.TrimSpace(stack[1].Operation.StringValue))
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}
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return stack[0], nil
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}