events_filter.go

 
/*
Copyright © 2022 Pavel Tisnovsky

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/



package
 
main



import
 
(

	
"fmt"


	
"go/scanner"

	
"go/token"


)

expression that we need to evaluate

 
const
 
source
 
=
 
`
confidence > 1 && (severity-1) >= 2 && priority < severity*2-1
`



func
 
main
(
)
 
{

scanner object (lexer)

 
	
var
 
s
 
scanner
.
Scanner

structure that represents set of source file(s)

 
	
fset
 
:=
 
token
.
NewFileSet
(
)

info about source file

 
	
file
 
:=
 
fset
.
AddFile
(
""
,
 
fset
.
Base
(
)
,
 
len
(
source
)
)

initialize the scanner

 
	
s
.
Init
(
file
,
 
[
]
byte
(
source
)
,
 
nil
,
 
scanner
.
ScanComments
)

transform input expression into postfix notation

 
	
postfixExpression
 
:=
 
toRPN
(
s
)

fmt.Println(postfixExpression)

values that can be used in expression

 
	
values
 
:=
 
make
(
map
[
string
]
int
)

	
values
[
"confidence"
]
 
=
 
2

	
values
[
"severity"
]
 
=
 
3

	
values
[
"priority"
]
 
=
 
1

evaluate the expression represented in postfix notation

 
	
stack
,
 
err
 
:=
 
evaluate
(
postfixExpression
,
 
values
)

	
if
 
err
 
!=
 
nil
 
{

		
fmt
.
Println
(
err
)

		
return

	
}

print operand stack

 
	
printStack
(
stack
)


}