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‎.gitignore

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.*.sw[pnmo]

‎LICENSE

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Apache License
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‎Makefile

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.DEFAULT_GOAL := build
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build:
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go build ./...
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test:
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go test ./...
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test-verbose:
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go test -v ./...
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fmt:
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go fmt ./...
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vet:
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go vet ./...
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# the fact that this is even needed is idiotic but whatchugonnado #golang #fuckyouweknowbetter
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fix:
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find . -type f -iname "*.go" -exec goimports -w {} +
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clean:
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go clean -x ./...
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.PHONY: build test fmt vet

‎README.md

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# integer-interval-expressions-go
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A Go library for parsing integer interval expressions such as `1,3-5,7-`
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These kinds of expressions are commonly seen in application contexts such as page selectors
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in print dialogs, or field selector in the CLI `cut` tool, and so on. This library
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provides support for parsing and utilizing such expressions in wide variety of
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application contexts.
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Internally, the library parses an input string into an abstract logical expression,
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which can be then evaluated with integer values to determine whether those
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values lie in any of the specified intervals. The parsed expressions do not contain
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any actual integer sequences, which allows for small memory usage and support for
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infinite ranges
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# Install
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Add the library into your project:
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$ go get github.com/MawKKe/integer-interval-expressions-go@latest
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then import the library in your application:
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import (
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...
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intervals "github.com/MawKKe/integer-interval-expressions-go"
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...
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)
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# Usage
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The library is quite simple to use. The primary function is `ParseExpression`
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which takes a string and returns the parsed intervals expression as an abstract
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`Expression` object:
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```Go
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inputString := "1,3-5,7-"
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myExpr, err := intervals.ParseExpression(inputString)
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if err != nil {
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fmt.Println("error:", err)
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return
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}
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fmt.Println("got valid expression:", myExpr)
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```
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Now you can evaluate the expression with various values:
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```Go
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myExpr.Matches(1) // == true
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myExpr.Matches(2) // == false
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myExpr.Matches(3) // == true
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myExpr.Matches(4) // == true
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myExpr.Matches(6) // == false
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myExpr.Matches(7) // == true
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myExpr.Matches(8) // == true
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myExpr.Matches(9) // == true, is so for all values >=7
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```
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As you see, the expression evaluates to true only on the specified integer
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intervals.
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**NOTE**: The `ParseExpression()` is merely a convenience function, while the
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actual work is performed by `ParseExpressionWithOptions()`. The difference is
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that the latter accepts a `ParseOptions` struct in addition to the input
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string; the options can be used for adjusting the operation of the parser to
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suit your needs. See the `go doc` documentation for more information. You may
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also be interested in the example and test functions in `expr_test.go`
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Thats pretty much all there is to it. How you actually use this functionality
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is up to you. A typical use case is to iterate your application data entries
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and check each one against the expression:
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```Go
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for _, page := range MyDocument.Pages {
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if myExpr.Matches(page.Number){
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PrintPage(page)
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}
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}
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```
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etc.
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## Syntax
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An intervals expression consists of sequence of individual subexpressions.
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A subexpression describes a continuous range of integral values (i.e an
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interval). A single subexpression string contains one of the following:
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- an single integer, for example `1`: only the value 1.
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- an integer, a dash, and another integer, for example `3-5`: values 3,4 and 5.
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- an integer and a dash, for example `7-`: denotes all integers from 7 to
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infinity (i.e 7,8,9,...)
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The intervals expression is consists of subexpressions joined by a delimiter
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character. By default, a comma (`","`) is used as the delimiter (although a
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custom delimiter can be specified via the `ParseOptions` structure). For
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example, the expression `1,3-5,7-` can be understood to contain three
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subexpressions: `1`, `3-5` and `7-`. Note that the interval expression
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string does not need to contain any subexpressions, which means that `""` and
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`",,,,"` are valid inputs. However, both of these parse into an `Expression`
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structure containing 0 subexpressions and are, as such, rather useless.
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Semantically, a single subexpression is a predicate, and combining multiple
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predicates denotes a logical disjunction. The above expression thus states that
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we have three predicates and an overall expression:
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func a(x int) { return x == 1 } // "1"
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func b(x int) { return x >= 3 && x <= 5 } // "3-5"
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func c(x int) { return x >= 7 } // "7-"
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func expr(x int) { return a(x) || b(x) || c(x) }
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(However note that in the library internals the expressions are not actually
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represented this way.)
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**NOTE**: For now, the library does not support parsing expressions with spaces
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inside subexpressions, or between the subexpressions and delimiters. This may
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change in future version.
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## Optimization
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The expression parser will happily process an input containing duplicate or
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overlapping subexpressions. Likewise, the order of subexpressions is irrelevant
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to the parser. However, poorly constructed expressions may result in
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unsatisfactory `Expression.Match` performance. To overcome such issues, the
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`Expression` instance can be simplified via its `Normalize()` method. The
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method sorts the subexpression ranges and merges overlapping ones, producing a
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minimal set of subexpressions. The resulting new `Expression` should be
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semantically equivalent to the original, while being more performant from practical
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perspective.
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**NOTE**: The parser does not perform the normalization automatically, unless
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`ParseOptions::PostProcessNormalize` is set to true.
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**NOTE**: Normalization may significantly change how an `Expression` is
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represented in text form. See the documentation for `Expression.String()`
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## De-serialization
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An `Expression` object can be converted back to string form via the `String()`
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method. For non-normalized expressions the resulting string should match
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closely the original expression string (omitting any superfluous whitespace).
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With normalized expressions, the resulting string is unlikely to be anything
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like the original input expression unless the original expression was already
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in normal form (this is not a bug).
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# Dependencies
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The program is written in Go, version 1.18. It may compile with older compiler
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versions. The program does not have any third party dependencies.
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# License
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Copyright 2022 Markus Holmström (MawKKe)
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The works under this repository are licenced under Apache License 2.0.
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See file `LICENSE` for more information.
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# Contributing
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This project is hosted at https://github.com/MawKKe/integer-interval-expressions-go
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You are welcome to leave bug reports, fixes and feature requests. Thanks!
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‎go.mod

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module github.com/MawKKe/integer-interval-expressions-go
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go 1.18

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