139 lines
3.6 KiB
Plaintext
139 lines
3.6 KiB
Plaintext
= Expr
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Expressions calculator
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:authors: Celestino Amoroso
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:docinfo: shared
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:encoding: utf-8
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:toc: right
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:toclevels: 4
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//:toc-title: Indice Generale
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:icons: font
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:icon-set: fi
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:numbered:
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//:table-caption: Tabella
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//:figure-caption: Diagramma
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:docinfo1:
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:sectlinks:
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:sectanchors:
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:source-highlighter: rouge
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// :rouge-style: ThankfulEyes
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:rouge-style: gruvbox
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// :rouge-style: colorful
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//:rouge-style: monokay
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toc::[]
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== Expr
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_Expr_ is a GO package capable of analysing, interpreting and calculating expressions.
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=== Usage
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[source,go]
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----
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import (
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"fmt"
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"strings"
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"git.portale-stac.it/go-pkg/expr"
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)
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func main() {
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ctx := expr.NewSimpleVarStore()
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ctx.SetValue("var", int64(4))
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source := `(3-1)*(10/5) == var`
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r := strings.NewReader(source)
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scanner := expr.NewScanner(r, DefaultTranslations())
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parser := expr.NewParser(ctx)
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if ast, err := parser.parse(scanner); err == nil {
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if result, err := ast.eval(ctx); err == nil {
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fmt.Printf("%q -> %v [%T]\n", source, result, result)
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} else {
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fmt.Println("Error calculating the expression:", err)
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}
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} else {
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fmt.Println("Error parsing the expression:", err)
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}
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}
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----
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The above program is equivalent to the following one.
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[source,go]
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----
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import (
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"fmt"
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"git.portale-stac.it/go-pkg/expr"
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)
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func main() {
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ctx := expr.NewSimpleVarStore()
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ctx.SetValue("var", int64(4))
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source := `(3-1)*(10/5) == var`
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if result, err := expr.evalString(ctx, source); err == nil {
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fmt.Printf("%q -> %v [%T]\n", source, result, result)
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} else {
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fmt.Println("Error calculating the expression:", err)
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}
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}
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----
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=== Data types
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_Expr_ supports numerical, string, relational, and boolean expressions.
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==== Numbers
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Numbers can be integers (GO int64) and float (GO float64). In mixed operations involving integers and floats, integers are automatically promoted to floats.
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.Arithmetic operators
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[cols="^1,^2,6,4"]
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|===
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| Symbol | Operation | Description | Examples
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| `+` / `-` | _change sign_ | Change the sign of values | `-1` _[-1]_, `-(+2)` _[-2]_
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| `+` | _sum_ | Add two values | `-1 + 2` _[1]_, `4 + 0.5` _[4.5]_
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| `-` | _subtracion_ | Subtract the right value from the left one | `3 - 1` _[2]_, `4 - 0.5` _[3.5]_
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| `*` | _product_ | Multiply two values | `-1 * 2` _[-2]_, `4 * 0.5` _[2.0]_
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| `/` | _Division_ | Divide the left value by the right one | `-1 / 2` _[0]_, `1.0 / 2` _[0.5]_
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| `./` | _Float division_ | Force float division | `-1 ./ 2` _[-0.5]_
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| `%` | _Modulo_ | Remainder of the integer division | `5 % 2` _[1]_
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|===
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==== String
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Strings are character sequences enclosed between two double quote `"`.
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==== Boolean
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Boolean data type has two values only: _true_ and _false_. Relational and Boolean expressions produce a Boolean values.
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.Relational operators
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[cols="^1,^2,6,4"]
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|===
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| Symbol | Operation | Description | Examples
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| `<` | _Less_ | True if the left value is less than the right one | `5 < 2` _[false]_, `"a" < "b"` [true]
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| `\<=` | _Less or Greater_ | True if the left value is less or greater than the right one | `5 <= 2` _[false]_, `"b" <= "b"` [true]
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|===
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.Boolean operators
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[cols="^1,^2,6,4"]
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|===
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| Symbol | Operation | Description | Examples
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| `NOT` | _Not_ | True if the right value is false | `NOT true` _[false]_, `NOT (2 < 1)` _[true]_
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| `AND` / `&&` | _And_ | True if both left and right values are true | `false && true` _[false]_, `"a" < "b" AND NOT (2 < 1)` _[true]_
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| `OR` / `\|\|` | _Or_ | True if at least one of the left and right values integers true| `false or true` _[true]_, `"a" == "b" OR (2 == 1)` _[false]_
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|===
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