README.md

mini-compiler

The smallest compiler

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Step

1、Parsing

• Lexical analysis

input
  "(add 2 (subtract 4 2))"
ouput(Tokens)
  [
    { type: 'paren',  value: '('        },
    { type: 'name',   value: 'add'      },
    { type: 'number', value: '2'        },
    { type: 'paren',  value: '('        },
    { type: 'name',   value: 'subtract' },
    { type: 'number', value: '4'        },
    { type: 'number', value: '2'        },
    { type: 'paren',  value: ')'        },
    { type: 'paren',  value: ')'        },
  ]

• Syntactic analysis

input(Tokens)
  [
    { type: 'paren',  value: '('        },
    { type: 'name',   value: 'add'      },
    { type: 'number', value: '2'        },
    { type: 'paren',  value: '('        },
    { type: 'name',   value: 'subtract' },
    { type: 'number', value: '4'        },
    { type: 'number', value: '2'        },
    { type: 'paren',  value: ')'        },
    { type: 'paren',  value: ')'        },
  ]
ouput(AST)
  {
    type: 'Program',
    body: [{
      type: 'CallExpression',
      name: 'add',
      params: [{
        type: 'NumberLiteral',
        value: '2',
      }, {
        type: 'CallExpression',
        name: 'subtract',
        params: [{
          type: 'NumberLiteral',
          value: '4',
        }, {
          type: 'NumberLiteral',
          value: '2',
        }]
      }]
    }]
  }

2、Transformation

• Traversal AST

  depth-first

  input(AST)
  {
    type: 'Program',
    body: [{
      type: 'CallExpression',
      name: 'add',
      params: [{
        type: 'NumberLiteral',
        value: '2',
      }, {
        type: 'CallExpression',
        name: 'subtract',
        params: [{
          type: 'NumberLiteral',
          value: '4',
        }, {
          type: 'NumberLiteral',
          value: '2',
        }]
      }]
    }]
  }
  ouput(Traversal order)
  [
    "program-enter",
    "callExpression-enter",
    "numberLiteral-enter",
    "numberLiteral-exit",
    "callExpression-enter",
    "numberLiteral-enter",
    "numberLiteral-exit",
    "numberLiteral-enter",
    "numberLiteral-exit",
    "callExpression-exit",
    "callExpression-exit",
    "program-exit",
  ]

  • transformer AST

          Original AST            |      Transformed AST
  {                               | {
    type: 'Program',              |   type: 'Program',
    body: [{                      |   body: [{
      type: 'CallExpression',     |     type: 'ExpressionStatement',
      name: 'add',                |     expression: {
      params: [{                  |       type: 'CallExpression',
        type: 'NumberLiteral',    |       callee: {
        value: '2'                |         type: 'Identifier',
      }, {                        |         name: 'add'
        type: 'CallExpression',   |       },
        name: 'subtract',         |       arguments: [{
        params: [{                |         type: 'NumberLiteral',
          type: 'NumberLiteral',  |         value: '2'
          value: '4'              |       }, {
        }, {                      |         type: 'CallExpression',
          type: 'NumberLiteral',  |         callee: {
          value: '2'              |           type: 'Identifier',
        }]                        |           name: 'subtract'
      }]                          |         },
    }]                            |         arguments: [{
  }                               |           type: 'NumberLiteral',
                                  |           value: '4'
                                  |         }, {
                                  |           type: 'NumberLiteral',
                                  |           value: '2'
                                  |         }]
                                  |        }]
                                  |       }
                                  |    }]
                                  | }

3、Code Generator

input(AST)
{
  type: "Program",
  body: [
    {
      type: "ExpressionStatement",
      expression: {
        type: "CallExpression",
        callee: {
          type: "Identifier",
          name: "add",
        },
        arguments: [
          {
            type: "NumberLiteral",
            value: "2",
          },
          {
            type: "CallExpression",
            callee: {
              type: "Identifier",
              name: "subtract",
            },
            arguments: [
              {
                type: "NumberLiteral",
                value: "4",
              },
              {
                type: "NumberLiteral",
                value: "2",
              },
            ],
          },
        ],
      },
    },
  ],
}
output(code)
"add(2, subtract(4, 2));"

Summarize

compiler

1. input => tokenizer => tokens
2. tokens => parser => ast
3. ast => transformer => newAst
4. newAst => generator => output

Unlike the-super-tiny-compiler

• use Typescript
• use Vitest

🌸 grateful

This project is deeply inspired by the following great projects.

• the-super-tiny-compiler