diff --git a/config.json b/config.json index 168a1e3f..07e07666 100644 --- a/config.json +++ b/config.json @@ -1319,6 +1319,14 @@ "practices": [], "prerequisites": [], "difficulty": 5 + }, + { + "slug": "forth", + "name": "Forth", + "uuid": "9c362b0b-5ef0-4371-9f63-637dd35cb07e", + "practices": [], + "prerequisites": [], + "difficulty": 6 } ] }, diff --git a/exercises/practice/forth/.busted b/exercises/practice/forth/.busted new file mode 100644 index 00000000..86b84e7c --- /dev/null +++ b/exercises/practice/forth/.busted @@ -0,0 +1,5 @@ +return { + default = { + ROOT = { '.' } + } +} diff --git a/exercises/practice/forth/.docs/instructions.md b/exercises/practice/forth/.docs/instructions.md new file mode 100644 index 00000000..91ad26e6 --- /dev/null +++ b/exercises/practice/forth/.docs/instructions.md @@ -0,0 +1,23 @@ +# Instructions + +Implement an evaluator for a very simple subset of Forth. + +[Forth][forth] +is a stack-based programming language. +Implement a very basic evaluator for a small subset of Forth. + +Your evaluator has to support the following words: + +- `+`, `-`, `*`, `/` (integer arithmetic) +- `DUP`, `DROP`, `SWAP`, `OVER` (stack manipulation) + +Your evaluator also has to support defining new words using the customary syntax: `: word-name definition ;`. + +To keep things simple the only data type you need to support is signed integers of at least 16 bits size. + +You should use the following rules for the syntax: a number is a sequence of one or more (ASCII) digits, a word is a sequence of one or more letters, digits, symbols or punctuation that is not a number. +(Forth probably uses slightly different rules, but this is close enough.) + +Words are case-insensitive. + +[forth]: https://en.wikipedia.org/wiki/Forth_%28programming_language%29 diff --git a/exercises/practice/forth/.meta/config.json b/exercises/practice/forth/.meta/config.json new file mode 100644 index 00000000..7f32f9ee --- /dev/null +++ b/exercises/practice/forth/.meta/config.json @@ -0,0 +1,17 @@ +{ + "authors": [ + "ryanplusplus" + ], + "files": { + "solution": [ + "forth.lua" + ], + "test": [ + "forth_spec.lua" + ], + "example": [ + ".meta/example.lua" + ] + }, + "blurb": "Implement an evaluator for a very simple subset of Forth." +} diff --git a/exercises/practice/forth/.meta/example.lua b/exercises/practice/forth/.meta/example.lua new file mode 100644 index 00000000..7360d733 --- /dev/null +++ b/exercises/practice/forth/.meta/example.lua @@ -0,0 +1,70 @@ +local function eval_definition(definition, user_words) + for name, body in definition:gmatch(': (%S+)%s+(.+) ;') do + assert(not tonumber(name)) + user_words[name:lower()] = body:gsub('%S+', function(s) + return user_words[s] or s + end) + end +end + +local function pop(stack) + assert(#stack > 0) + return table.remove(stack) +end + +local function push(stack, element) + assert(element ~= nil) + table.insert(stack, element) +end + +local function eval_code(code, stack, user_words) + for element in code:lower():gmatch('%S+') do + if user_words[element] then + eval_code(user_words[element], stack, user_words) + else + if element == '+' then + push(stack, pop(stack) + pop(stack)) + elseif element == '-' then + push(stack, -pop(stack) + pop(stack)) + elseif element == '*' then + push(stack, pop(stack) * pop(stack)) + elseif element == '/' then + local divisor = pop(stack) + local dividend = pop(stack) + assert(divisor ~= 0) + push(stack, dividend // divisor) + elseif element == 'dup' then + push(stack, stack[#stack]) + elseif element == 'drop' then + pop(stack) + elseif element == 'swap' then + local e1, e2 = pop(stack), pop(stack) + push(stack, e1) + push(stack, e2) + elseif element == 'over' then + push(stack, stack[#stack - 1]) + else + push(stack, tonumber(element)) + end + end + end +end + +local function eval_instruction(chunk, stack, user_words) + if chunk:sub(1, 1) == ':' then + eval_definition(chunk, user_words) + else + eval_code(chunk, stack, user_words) + end +end + +local function evaluate(instructions) + local stack = {} + local user_words = {} + for _, instruction in ipairs(instructions) do + eval_instruction(instruction, stack, user_words) + end + return stack +end + +return { evaluate = evaluate } diff --git a/exercises/practice/forth/.meta/tests.toml b/exercises/practice/forth/.meta/tests.toml new file mode 100644 index 00000000..c9c1d637 --- /dev/null +++ b/exercises/practice/forth/.meta/tests.toml @@ -0,0 +1,157 @@ +# This is an auto-generated file. +# +# Regenerating this file via `configlet sync` will: +# - Recreate every `description` key/value pair +# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications +# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion) +# - Preserve any other key/value pair +# +# As user-added comments (using the # character) will be removed when this file +# is regenerated, comments can be added via a `comment` key. + +[9962203f-f00a-4a85-b404-8a8ecbcec09d] +description = "parsing and numbers -> numbers just get pushed onto the stack" + +[fd7a8da2-6818-4203-a866-fed0714e7aa0] +description = "parsing and numbers -> pushes negative numbers onto the stack" + +[9e69588e-a3d8-41a3-a371-ea02206c1e6e] +description = "addition -> can add two numbers" + +[52336dd3-30da-4e5c-8523-bdf9a3427657] +description = "addition -> errors if there is nothing on the stack" + +[06efb9a4-817a-435e-b509-06166993c1b8] +description = "addition -> errors if there is only one value on the stack" + +[09687c99-7bbc-44af-8526-e402f997ccbf] +description = "subtraction -> can subtract two numbers" + +[5d63eee2-1f7d-4538-b475-e27682ab8032] +description = "subtraction -> errors if there is nothing on the stack" + +[b3cee1b2-9159-418a-b00d-a1bb3765c23b] +description = "subtraction -> errors if there is only one value on the stack" + +[5df0ceb5-922e-401f-974d-8287427dbf21] +description = "multiplication -> can multiply two numbers" + +[9e004339-15ac-4063-8ec1-5720f4e75046] +description = "multiplication -> errors if there is nothing on the stack" + +[8ba4b432-9f94-41e0-8fae-3b3712bd51b3] +description = "multiplication -> errors if there is only one value on the stack" + +[e74c2204-b057-4cff-9aa9-31c7c97a93f5] +description = "division -> can divide two numbers" + +[54f6711c-4b14-4bb0-98ad-d974a22c4620] +description = "division -> performs integer division" + +[a5df3219-29b4-4d2f-b427-81f82f42a3f1] +description = "division -> errors if dividing by zero" + +[1d5bb6b3-6749-4e02-8a79-b5d4d334cb8a] +description = "division -> errors if there is nothing on the stack" + +[d5547f43-c2ff-4d5c-9cb0-2a4f6684c20d] +description = "division -> errors if there is only one value on the stack" + +[ee28d729-6692-4a30-b9be-0d830c52a68c] +description = "combined arithmetic -> addition and subtraction" + +[40b197da-fa4b-4aca-a50b-f000d19422c1] +description = "combined arithmetic -> multiplication and division" + +[c5758235-6eef-4bf6-ab62-c878e50b9957] +description = "dup -> copies a value on the stack" + +[f6889006-5a40-41e7-beb3-43b09e5a22f4] +description = "dup -> copies the top value on the stack" + +[40b7569c-8401-4bd4-a30d-9adf70d11bc4] +description = "dup -> errors if there is nothing on the stack" + +[1971da68-1df2-4569-927a-72bf5bb7263c] +description = "drop -> removes the top value on the stack if it is the only one" + +[8929d9f2-4a78-4e0f-90ad-be1a0f313fd9] +description = "drop -> removes the top value on the stack if it is not the only one" + +[6dd31873-6dd7-4cb8-9e90-7daa33ba045c] +description = "drop -> errors if there is nothing on the stack" + +[3ee68e62-f98a-4cce-9e6c-8aae6c65a4e3] +description = "swap -> swaps the top two values on the stack if they are the only ones" + +[8ce869d5-a503-44e4-ab55-1da36816ff1c] +description = "swap -> swaps the top two values on the stack if they are not the only ones" + +[74ba5b2a-b028-4759-9176-c5c0e7b2b154] +description = "swap -> errors if there is nothing on the stack" + +[dd52e154-5d0d-4a5c-9e5d-73eb36052bc8] +description = "swap -> errors if there is only one value on the stack" + +[a2654074-ba68-4f93-b014-6b12693a8b50] +description = "over -> copies the second element if there are only two" + +[c5b51097-741a-4da7-8736-5c93fa856339] +description = "over -> copies the second element if there are more than two" + +[6e1703a6-5963-4a03-abba-02e77e3181fd] +description = "over -> errors if there is nothing on the stack" + +[ee574dc4-ef71-46f6-8c6a-b4af3a10c45f] +description = "over -> errors if there is only one value on the stack" + +[ed45cbbf-4dbf-4901-825b-54b20dbee53b] +description = "user-defined words -> can consist of built-in words" + +[2726ea44-73e4-436b-bc2b-5ff0c6aa014b] +description = "user-defined words -> execute in the right order" + +[9e53c2d0-b8ef-4ad8-b2c9-a559b421eb33] +description = "user-defined words -> can override other user-defined words" + +[669db3f3-5bd6-4be0-83d1-618cd6e4984b] +description = "user-defined words -> can override built-in words" + +[588de2f0-c56e-4c68-be0b-0bb1e603c500] +description = "user-defined words -> can override built-in operators" + +[ac12aaaf-26c6-4a10-8b3c-1c958fa2914c] +description = "user-defined words -> can use different words with the same name" + +[53f82ef0-2750-4ccb-ac04-5d8c1aefabb1] +description = "user-defined words -> can define word that uses word with the same name" + +[35958cee-a976-4a0f-9378-f678518fa322] +description = "user-defined words -> cannot redefine non-negative numbers" + +[df5b2815-3843-4f55-b16c-c3ed507292a7] +description = "user-defined words -> cannot redefine negative numbers" + +[5180f261-89dd-491e-b230-62737e09806f] +description = "user-defined words -> errors if executing a non-existent word" + +[3c8bfef3-edbb-49c1-9993-21d4030043cb] +description = "user-defined words -> only defines locally" + +[7b83bb2e-b0e8-461f-ad3b-96ee2e111ed6] +description = "case-insensitivity -> DUP is case-insensitive" + +[339ed30b-f5b4-47ff-ab1c-67591a9cd336] +description = "case-insensitivity -> DROP is case-insensitive" + +[ee1af31e-1355-4b1b-bb95-f9d0b2961b87] +description = "case-insensitivity -> SWAP is case-insensitive" + +[acdc3a49-14c8-4cc2-945d-11edee6408fa] +description = "case-insensitivity -> OVER is case-insensitive" + +[5934454f-a24f-4efc-9fdd-5794e5f0c23c] +description = "case-insensitivity -> user-defined words are case-insensitive" + +[037d4299-195f-4be7-a46d-f07ca6280a06] +description = "case-insensitivity -> definitions are case-insensitive" diff --git a/exercises/practice/forth/forth.lua b/exercises/practice/forth/forth.lua new file mode 100644 index 00000000..f9b9f92a --- /dev/null +++ b/exercises/practice/forth/forth.lua @@ -0,0 +1,5 @@ +local function evaluate(instructions) + +end + +return { evaluate = evaluate } diff --git a/exercises/practice/forth/forth_spec.lua b/exercises/practice/forth/forth_spec.lua new file mode 100644 index 00000000..d55159a0 --- /dev/null +++ b/exercises/practice/forth/forth_spec.lua @@ -0,0 +1,236 @@ +local forth = require('forth') + +describe('forth', function() + it('numbers just get pushed onto the stack', function() + assert.are.same({ 1, 2, 3, 4, 5 }, forth.evaluate({ '1 2 3 4 5' })) + end) + + it('pushes negative numbers onto the stack', function() + assert.are.same({ -1, -2, -3, -4, -5 }, forth.evaluate({ '-1 -2 -3 -4 -5' })) + end) + + it('can add two numbers', function() + assert.are.same({ 3 }, forth.evaluate({ '1 2 +' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ '+' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 +' }) + end) + end) + + it('can subtract two numbers', function() + assert.are.same({ -1 }, forth.evaluate({ '3 4 -' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ '-' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 -' }) + end) + end) + + it('can multiply two numbers', function() + assert.are.same({ 8 }, forth.evaluate({ '2 4 *' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ '*' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 *' }) + end) + end) + + it('can divide two numbers', function() + assert.are.same({ 4 }, forth.evaluate({ '12 3 /' })) + end) + + it('performs integer division', function() + assert.are.same({ 2 }, forth.evaluate({ '8 3 /' })) + end) + + it('errors if dividing by zero', function() + assert.has.error(function() + forth.evaluate({ '4 0 /' }) + end) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ '/' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 /' }) + end) + end) + + it('addition and subtraction', function() + assert.are.same({ -1 }, forth.evaluate({ '1 2 + 4 -' })) + end) + + it('multiplication and division', function() + assert.are.same({ 2 }, forth.evaluate({ '2 4 * 3 /' })) + end) + + it('copies a value on the stack', function() + assert.are.same({ 1, 1 }, forth.evaluate({ '1 dup' })) + end) + + it('copies the top value on the stack', function() + assert.are.same({ 1, 2, 2 }, forth.evaluate({ '1 2 dup' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ 'dup' }) + end) + end) + + it('removes the top value on the stack if it is the only one', function() + assert.are.same({}, forth.evaluate({ '1 drop' })) + end) + + it('removes the top value on the stack if it is not the only one', function() + assert.are.same({ 1 }, forth.evaluate({ '1 2 drop' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ 'drop' }) + end) + end) + + it('swaps the top two values on the stack if they are the only ones', function() + assert.are.same({ 2, 1 }, forth.evaluate({ '1 2 swap' })) + end) + + it('swaps the top two values on the stack if they are not the only ones', function() + assert.are.same({ 1, 3, 2 }, forth.evaluate({ '1 2 3 swap' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ 'swap' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 swap' }) + end) + end) + + it('copies the second element if there are only two', function() + assert.are.same({ 1, 2, 1 }, forth.evaluate({ '1 2 over' })) + end) + + it('copies the second element if there are more than two', function() + assert.are.same({ 1, 2, 3, 2 }, forth.evaluate({ '1 2 3 over' })) + end) + + it('errors if there is nothing on the stack', function() + assert.has.error(function() + forth.evaluate({ 'over' }) + end) + end) + + it('errors if there is only one value on the stack', function() + assert.has.error(function() + forth.evaluate({ '1 over' }) + end) + end) + + it('can consist of built-in words', function() + assert.are.same({ 1, 1, 1 }, forth.evaluate({ ': dup-twice dup dup ;', '1 dup-twice' })) + end) + + it('execute in the right order', function() + assert.are.same({ 1, 2, 3 }, forth.evaluate({ ': countup 1 2 3 ;', 'countup' })) + end) + + it('can override other user-defined words', function() + assert.are.same({ 1, 1, 1 }, forth.evaluate({ ': foo dup ;', ': foo dup dup ;', '1 foo' })) + end) + + it('can override built-in words', function() + assert.are.same({ 1, 1 }, forth.evaluate({ ': swap dup ;', '1 swap' })) + end) + + it('can override built-in operators', function() + assert.are.same({ 12 }, forth.evaluate({ ': + * ;', '3 4 +' })) + end) + + it('can use different words with the same name', function() + assert.are.same({ 5, 6 }, forth.evaluate({ ': foo 5 ;', ': bar foo ;', ': foo 6 ;', 'bar foo' })) + end) + + it('can define word that uses word with the same name', function() + assert.are.same({ 11 }, forth.evaluate({ ': foo 10 ;', ': foo foo 1 + ;', 'foo' })) + end) + + it('cannot redefine non-negative numbers', function() + assert.has.error(function() + forth.evaluate({ ': 1 2 ;' }) + end) + end) + + it('cannot redefine negative numbers', function() + assert.has.error(function() + forth.evaluate({ ': -1 2 ;' }) + end) + end) + + it('errors if executing a non-existent word', function() + assert.has.error(function() + forth.evaluate({ 'foo' }) + end) + end) + + it('only defines locally', function() + assert.are.same({ 0 }, forth.evaluate({ ': + - ;', '1 1 +' })) + assert.are.same({ 2 }, forth.evaluate({ '1 1 +' })) + end) + + it('DUP is case-insensitive', function() + assert.are.same({ 1, 1, 1, 1 }, forth.evaluate({ '1 DUP Dup dup' })) + end) + + it('DROP is case-insensitive', function() + assert.are.same({ 1 }, forth.evaluate({ '1 2 3 4 DROP Drop drop' })) + end) + + it('SWAP is case-insensitive', function() + assert.are.same({ 2, 3, 4, 1 }, forth.evaluate({ '1 2 SWAP 3 Swap 4 swap' })) + end) + + it('OVER is case-insensitive', function() + assert.are.same({ 1, 2, 1, 2, 1 }, forth.evaluate({ '1 2 OVER Over over' })) + end) + + it('user-defined words are case-insensitive', function() + assert.are.same({ 1, 1, 1, 1 }, forth.evaluate({ ': foo dup ;', '1 FOO Foo foo' })) + end) + + it('definitions are case-insensitive', function() + assert.are.same({ 1, 1, 1, 1 }, forth.evaluate({ ': SWAP DUP Dup dup ;', '1 swap' })) + end) +end)