143 lines
3.3 KiB
Markdown
143 lines
3.3 KiB
Markdown
---
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id: constants-and-variables
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title: Constants & Variables
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---
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import Syntax from '@theme/Syntax';
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The next building block after types are *constants* and *variables*.
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## Constants
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Constants are immutable by design, which means their values cannot be
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reassigned. Put in another way, they can be assigned once, at their
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declaration. When defining a constant you need to provide a `name`,
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`type` and a `value`:
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<Syntax syntax="pascaligo">
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```pascaligo group=a
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const age : int = 25
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```
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You can evaluate the constant definition above using the following CLI
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command:
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```shell
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ligo evaluate-value gitlab-pages/docs/language-basics/src/variables-and-constants/const.ligo age
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# Outputs: 25
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```
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</Syntax>
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<Syntax syntax="cameligo">
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```cameligo group=a
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let age : int = 25
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```
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You can evaluate the constant definition above using the following CLI
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command:
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```shell
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ligo evaluate-value gitlab-pages/docs/language-basics/src/variables-and-constants/const.mligo age
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# Outputs: 25
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```
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</Syntax>
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<Syntax syntax="reasonligo">
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```reasonligo group=a
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let age : int = 25;
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```
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You can evaluate the constant definition above using the following CLI
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command:
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```shell
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ligo evaluate-value gitlab-pages/docs/language-basics/src/variables-and-constants/const.religo age
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# Outputs: 25
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```
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</Syntax>
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## Variables
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<Syntax syntax="pascaligo">
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Variables, unlike constants, are *mutable*. They cannot be declared in
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a *global scope*, but they can be declared and used within functions,
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or as function parameters.
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> ⚠️ Please be wary that mutation only works within the function scope
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> itself, values outside of the function scope will not be
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> affected. In other words, when a function is called, its arguments
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> are copied, *as well as the environment*. Any side-effect to that
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> environment is therefore lost when the function returns.
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```pascaligo group=b
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// The following is invalid: use `const` for global values instead.
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// var four : int := 4
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function add (const a : int; const b : int) : int is
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block {
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var c : int := a + 2*b;
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c := c - b
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} with c
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```
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> ⚠️ Notice the assignment operator `:=` for `var`, instead of `=` for
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> constants.
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You can run the `add` function defined above using the LIGO compiler
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like this:
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```shell
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ligo run-function gitlab-pages/docs/language-basics/src/variables-and-constants/add.ligo add '(1,1)'
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# Outputs: 2
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```
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</Syntax>
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<Syntax syntax="cameligo">
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As expected in the pure subset of a functional language, CameLIGO only
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features *constant values*: once they are declared, the value cannot
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be changed (or "mutated").
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```cameligo group=c
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let add (a : int) (b : int) : int =
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let c : int = a + b in c
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```
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You can run the `add` function defined above using the LIGO compiler
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like this:
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```shell
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ligo run-function gitlab-pages/docs/language-basics/src/variables-and-constants/add.mligo add '(1,1)'
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# Outputs: 2
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```
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</Syntax>
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<Syntax syntax="reasonligo">
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As expected in the pure subset of a functional language, ReasonLIGO
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only features *constant values*: once they are declared, the value
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cannot be changed (or "mutated").
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```reasonligo group=c
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let add = ((a, b): (int, int)): int => {
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let c : int = a + b;
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c;
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};
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```
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You can run the `add` function defined above using the LIGO compiler
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like this:
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```shell
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ligo run-function gitlab-pages/docs/language-basics/src/variables-and-constants/add.religo add '(1,1)'
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# Outputs: 2
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```
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</Syntax>
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