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Add resistor-color-trio exercise (#187)
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‎config.json‎

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"prerequisites": [],
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"difficulty": 6
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},
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{
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"slug": "resistor-color-trio",
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"name": "Resistor Color Trio",
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"uuid": "a3763bb0-6eb4-4cec-8879-6069fb1418a2",
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"practices": [],
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"prerequisites": [],
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"difficulty": 6
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},
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{
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"slug": "book-store",
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"name": "Book Store",

‎exercises/practice/resistor-color-duo/.docs/instructions.append.md‎

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If you work locally or in Lean's [online playground][playground], you will get instant feedback on any error reported by `#guard_msgs` through Lean InfoView.
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~~~~exercism/caution
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For practical reasons, the online test runner does not currently have support to the built-in `Lean` library.
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This means that, although you are free to import this library, or any module within it, when working locally or in Lean's online playground, this will cause a solution to fail when submitted to exercism.
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The online test runner does not currently support importing the full `Lean` meta-programming library.
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While you are free to use any features available in Lean by default, including those within the `Lean` namespace, adding `import Lean` or importing specific modules from the `Lean` namespace will cause your submission to fail when submitted to Exercism.
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Note that this library is not necessary to solve the exercise.
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Note that importing the Lean library is not necessary to solve this exercise.
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~~~~
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[macro-reference]: https://lean-lang.org/doc/reference/latest/Notations-and-Macros/#language-extension
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[guard-msgs]: https://lean-lang.org/doc/reference/latest/Interacting-with-Lean/#hash-guard_msgs
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[eval]: https://lean-lang.org/doc/reference/latest/Interacting-with-Lean/#hash-eval
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[playground]: https://live.lean-lang.org/
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[playground]: https://live.lean-lang.org/

‎exercises/practice/resistor-color-trio/.docs/instructions.append.md‎

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# Instructions append
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## Defining syntax
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~~~~exercism/caution
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This exercise is intended as a continuation of [`Resistor Color Duo`][resistor-color-duo] and builds upon it.
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Although you may solve practice exercises in any order, we encourage you to follow the suggested sequence.
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[resistor-color-duo]: https://exercism.org/tracks/lean/exercises/resistor-color-duo
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~~~~
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In this exercise, you are given syntax for colors already predefined using the `c*` prefix, e.g., `c*black`.
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You must then define syntax that associates a sequence of colors to a resistance value with its SI unit, possibly with a metric prefix, according to the instructions.
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The colors are within `*[[` and `]]` and separated by `, `, e.g., `*[[c*black, c*yellow, c*violet]]`.
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This task will likely require you to use either notations or macros.
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You might want to check a [reference][macro-reference].
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Because new syntax is expanded at compile time, any test would fail to compile unless all the required syntax is defined.
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For this reason, instead of relying on traditional runtime tests, we use [`#guard_msgs`][guard-msgs].
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This command compares a given docstring with a message generated by another command, in this case [`#eval`][eval], and reports an error if they are different.
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You may consider the absence of an error as a passing test.
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If you work locally or in Lean's [online playground][playground], you will get instant feedback on any error reported by `#guard_msgs` through Lean InfoView.
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~~~~exercism/note
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The resistance value should be output using the unit `Ω` (ohm).
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This unicode character can be generated locally on in Lean's online playground with the shortcut `\ohm`.
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If you are working in Exercism's online editor, feel free to copy the character from the instructions.
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~~~~
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~~~~exercism/caution
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The online test runner does not currently support importing the full `Lean` meta-programming library.
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While you are free to use any features available in Lean by default, including those within the `Lean` namespace, adding `import Lean` or importing specific modules from the `Lean` namespace will cause your submission to fail when submitted to Exercism.
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Note that importing the Lean library is not necessary to solve this exercise.
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~~~~
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[macro-reference]: https://lean-lang.org/doc/reference/latest/Notations-and-Macros/#language-extension
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[guard-msgs]: https://lean-lang.org/doc/reference/latest/Interacting-with-Lean/#hash-guard_msgs
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[eval]: https://lean-lang.org/doc/reference/latest/Interacting-with-Lean/#hash-eval
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[playground]: https://live.lean-lang.org/

‎exercises/practice/resistor-color-trio/.docs/instructions.md‎

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# Instructions
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If you want to build something using a Raspberry Pi, you'll probably use _resistors_.
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For this exercise, you need to know only three things about them:
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- Each resistor has a resistance value.
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- Resistors are small - so small in fact that if you printed the resistance value on them, it would be hard to read.
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To get around this problem, manufacturers print color-coded bands onto the resistors to denote their resistance values.
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- Each band acts as a digit of a number.
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For example, if they printed a brown band (value 1) followed by a green band (value 5), it would translate to the number 15.
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In this exercise, you are going to create a helpful program so that you don't have to remember the values of the bands.
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The program will take 3 colors as input, and outputs the correct value, in ohms.
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The color bands are encoded as follows:
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- black: 0
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- brown: 1
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- red: 2
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- orange: 3
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- yellow: 4
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- green: 5
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- blue: 6
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- violet: 7
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- grey: 8
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- white: 9
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In Resistor Color Duo you decoded the first two colors.
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For instance: orange-orange got the main value `33`.
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The third color stands for how many zeros need to be added to the main value.
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The main value plus the zeros gives us a value in ohms.
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For the exercise it doesn't matter what ohms really are.
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For example:
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- orange-orange-black would be 33 and no zeros, which becomes 33 ohms.
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- orange-orange-red would be 33 and 2 zeros, which becomes 3300 ohms.
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- orange-orange-orange would be 33 and 3 zeros, which becomes 33000 ohms.
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(If Math is your thing, you may want to think of the zeros as exponents of 10.
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If Math is not your thing, go with the zeros.
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It really is the same thing, just in plain English instead of Math lingo.)
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This exercise is about translating the colors into a label:
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> "... ohms"
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So an input of `"orange", "orange", "black"` should return:
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> "33 ohms"
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When we get to larger resistors, a [metric prefix][metric-prefix] is used to indicate a larger magnitude of ohms, such as "kiloohms".
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That is similar to saying "2 kilometers" instead of "2000 meters", or "2 kilograms" for "2000 grams".
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For example, an input of `"orange", "orange", "orange"` should return:
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> "33 kiloohms"
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[metric-prefix]: https://en.wikipedia.org/wiki/Metric_prefix

‎exercises/practice/resistor-color-trio/.meta/Example.lean‎

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import Extra
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open Lean Syntax Macro
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namespace ResistorColorTrio
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structure ResistorValue where
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text : String
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instance : Repr ResistorValue where
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reprPrec v _ := f!"{v.text}"
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macro_rules
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| `(*[[ $colors,* ]]) => do
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match colors.getElems.take 3 with
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| #[c₁, c₂, c₃] =>
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match c₁, c₂, c₃ with
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| `(ident| $v₁), `(ident| $v₂), `(ident| $v₃) =>
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let str ← `(
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let total := ((10 * ↑$v₁) + ↑$v₂) * (10 ^ ↑$v₃)
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if total >= 1_000_000_000 then
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let resistance := total / 1_000_000_000
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s!"{resistance} GΩ"
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else if total >= 1_000_000 then
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let resistance := total / 1_000_000
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s!"{resistance} MΩ"
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else if total >= 1_000 then
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let resistance := total / 1_000
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s!"{resistance} kΩ"
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else s!"{total} Ω"
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)
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`(ResistorValue.mk $str)
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| _ => Lean.Macro.throwUnsupported
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end ResistorColorTrio

‎exercises/practice/resistor-color-trio/.meta/config.json‎

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{
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"authors": [
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"oxe-i"
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],
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"files": {
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"solution": [
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"ResistorColorTrio.lean"
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],
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"test": [
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"ResistorColorTrioTest.lean"
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],
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"example": [
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".meta/Example.lean"
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]
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},
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"blurb": "Convert color codes, as used on resistors, to a human-readable label.",
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"source": "Maud de Vries, Erik Schierboom",
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"source_url": "https://github.com/exercism/problem-specifications/issues/1549"
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}

‎exercises/practice/resistor-color-trio/.meta/tests.toml‎

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# This is an auto-generated file.
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#
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# Regenerating this file via `configlet sync` will:
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# - Recreate every `description` key/value pair
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# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
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# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
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# - Preserve any other key/value pair
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#
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# As user-added comments (using the # character) will be removed when this file
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# is regenerated, comments can be added via a `comment` key.
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[d6863355-15b7-40bb-abe0-bfb1a25512ed]
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description = "Orange and orange and black"
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[1224a3a9-8c8e-4032-843a-5224e04647d6]
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description = "Blue and grey and brown"
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[b8bda7dc-6b95-4539-abb2-2ad51d66a207]
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description = "Red and black and red"
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[5b1e74bc-d838-4eda-bbb3-eaba988e733b]
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description = "Green and brown and orange"
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[f5d37ef9-1919-4719-a90d-a33c5a6934c9]
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description = "Yellow and violet and yellow"
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[5f6404a7-5bb3-4283-877d-3d39bcc33854]
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description = "Blue and violet and blue"
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[7d3a6ab8-e40e-46c3-98b1-91639fff2344]
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description = "Minimum possible value"
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[ca0aa0ac-3825-42de-9f07-dac68cc580fd]
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description = "Maximum possible value"
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[0061a76c-903a-4714-8ce2-f26ce23b0e09]
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description = "First two colors make an invalid octal number"
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[30872c92-f567-4b69-a105-8455611c10c4]
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description = "Ignore extra colors"

‎exercises/practice/resistor-color-trio/Extra.lean‎

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declare_syntax_cat colors
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syntax "c*" ident : colors
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macro_rules
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| `(colors|c*black) => `((0 : Fin 10))
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| `(colors|c*brown) => `((1 : Fin 10))
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| `(colors|c*red) => `((2 : Fin 10))
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| `(colors|c*orange) => `((3 : Fin 10))
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| `(colors|c*yellow) => `((4 : Fin 10))
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| `(colors|c*green) => `((5 : Fin 10))
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| `(colors|c*blue) => `((6 : Fin 10))
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| `(colors|c*violet) => `((7 : Fin 10))
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| `(colors|c*grey) => `((8 : Fin 10))
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| `(colors|c*white) => `((9 : Fin 10))
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syntax "*[[" colors,* "]]" : term

‎exercises/practice/resistor-color-trio/ResistorColorTrio.lean‎

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import Extra
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/-
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You are given syntax for colors already predefined using the `c*` prefix, e.g., `c*black`.
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You must then define syntax that associates a sequence of colors to a number, according to the instructions.
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The colors are within `*[[` and `]]` and separated by `, `, e.g., `*[[c*black, c*yellow, c*violet]]`.
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Note that the online test runner does not have support to the `Lean` library.
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Any solution that uses it will fail when submitted to exercism, even if correct.
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This library is not necessary to solve the exercise.
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Macros and notations are not qualified by namespace.
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For this reason, this exercise does not define a namespace.
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-/

‎exercises/practice/resistor-color-trio/ResistorColorTrioTest.lean‎

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import LeanTest
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import ResistorColorTrio
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open LeanTest
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/--
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info: 33 Ω
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*orange, c*orange, c*black]]
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/--
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info: 680 Ω
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*blue, c*grey, c*brown]]
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/--
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info: 2 kΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*red, c*black, c*red]]
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/--
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info: 51 kΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*green, c*brown, c*orange]]
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/--
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info: 470 kΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*yellow, c*violet, c*yellow]]
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/--
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info: 67 MΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*blue, c*violet, c*blue]]
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/--
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info: 0 Ω
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*black, c*black, c*black]]
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/--
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info: 99 GΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*white, c*white, c*white]]
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/--
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info: 8 Ω
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*black, c*grey, c*black]]
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/--
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info: 650 kΩ
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-/
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#guard_msgs(info, drop all) in
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#eval *[[c*blue, c*green, c*yellow, c*orange]]
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def main : IO UInt32 := do
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runTestSuitesWithExitCode []

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