chimpanzee

chimpanzee

Chimpanzee is a library for pattern matching tree, especially ASTs. This documentation covers the important features, but is not exhaustive.

Installation

npm install chimpanzee

Getting Started

import { match, traverse, capture } from "chimpanzee";

const input = {
  hello: "world"
}

const schema = traverse({
  hello: capture()
})

const result = match(schema, input);

//result is Match { value: { hello: "world" } }

Usage

Simple capturing: capture()

const input = {
  hello: "world"
}

const schema = traverse({
  hello: capture()
})

//result is Match { value: { hello: "world" } }

Named capturing: capture(alias)

const input = {
  hello: "world"
}

const schema = traverse({
  hello: capture("prop1")
})

//result is Match { value: { prop1: "world" } }

Mismatched Tree

const input = {
  hello: "world"
}

const schema = traverse({
  something: "else",
  hello: capture()
})

//result is Skip { message: "Expected something to be defined." }

Capture with predicate: captureIf(predicate)

const input = {
  hello: "world"
}

const schema = traverse({
  hello: captureIf(x => x === "world")
})

//result is Match { value: { hello: "world" } }

Capturing Types

const input = {
  name: "JPK",
  isHuman: true,
  age: 36,
  meta: { x: 100 },
  getCoordinates: () => "BLR"
}

const schema = traverse({
  name: string(),
  isHuman: bool(),
  age: number(),
  meta: object(),
  getCoordinates: func()
})

Capture a Literal

const input = {
  name: "JPK",
}

const schema = traverse({
  name: literal("JPK"),
})

Matching Arrays

const input = {
  myArray: [1, 2, 3]
}

const schema = traverse({ myArray: [number(), number(), number()] });

Nested

const input = {
  inner1: {
   hello: "world"
  }
}

const schema = traverse({
  inner1: {
    hello: capture()
   }
})

//result is Match { value: { inner1: { hello: "world" } } }

Merging with Parent (replace flag)

const input = {
  inner1: {
   hello: "world"
  }
}

const schema = traverse({
  inner1: {
    hello: capture()
   }
}, { replace: true })

//result is Match { value: { hello: "world" } }

Capturing and traversing Child Schema (Parent-Child)

const input = {
  level1: {
    level2: "hello world"
  }
}

const schema = traverse({
  level1: captureWithSchema(traverse({
    level2: capture("prop2")
  }), "prop1")
})

//result is Match { prop1: { level2: 'hello world', prop2: 'hello world' } }

Matching Any Schema: any(list)

const input = {
  level1: {
    level2: "world"
  }
}

schema1 = traverse({
  level4: capture("hello")
})

schema2 = traverse({
  level1: {
    level2: capture("hello")
  }
});

const schema = any([schema1, schema2]);

Matching nodes deeper in the tree: deep(schema)

const input = {
  level1: {
    prop1: "hello",
    level2: {
      level3: {
        prop2: "something"
      }
    },
    level2a: {
      level3a: {
        level4a: {
          level5a: {
            prop3: "world"
          }
        },
        level4b: "yoyo"
      }
    }
  }
}

const schema = traverse({
  level1: {
    level2a: deep(traverse({
      level5a: {
        prop3: capture()
      }
    }), "prop1")
  }
})

//result is Match { prop1: { prop3: 'world' } }

Matching undefined or empty: empty()

const input = {
  prop1: "hello",
  prop2: undefined
}

const schema = traverse({
  prop1: capture(),
  prop2: empty()
})

//result is Match export const result = { prop1: "hello" }

Matching the existence of a node: exists()

export const input = {
  hello: "world",
  prop1: "val1"
}

export const schema = traverse({
  hello: exists(),
  prop1: capture()
})

//This makes sure that hello exists. Or it returns a Skip.

Matching with Regex: regex()

const input = {
  hello: "world"
}

const schema = traverse({
  hello: regex(/^world$/)
})

Advanced

Property Modifier. Use this if your input tree isn't a simple object.

const input = {
  getItem(item) {
    return item === "hello" ? "world" : "nothing";
  }
}

const schema = traverse({
  hello: capture()
}, { modifier: (obj, key) => obj.getItem(key) })

Builders

Advanced features which let you:

• modify the result of the capture (builder.get)
• Pause traversing until another subtree finishes (builder.precondition)

In the following example, level1 matching waits until level2 is complete (builder.precondition). And then proceeds to build the result of level1 (builder.get).

export const input = {
  level1: {
    prop1: "hello",
  },
  level2: {
    prop2: "world"
  }
}

export const schema = traverse(
  {
    level1: traverse(
      {
        prop1: capture()
      },
      {
        builders: [{
          precondition: (obj, context) => context.parent.state && context.parent.state.prop2,
          get: (obj, context) => ({ prop3: `${context.state.prop1} ${context.parent.state.prop2}` })
        }]
      },
    ),
    level2: {
      prop2: capture(),
    },
  }
)

Builder Asserts

Generates a Fault which will stop the matching on the tree.

export const input = {
  prop1: "hello"
}

export const schema = traverse(
  {
    prop1: capture(),
  },
  {
    builders: [{
      asserts: [{ predicate: (obj, context) => context.state.prop1 !== "hello", error: "prop1 cannot be hello" }],
      get: (obj, context) => ({ prop1: context.state.prop1 + " world" })
    }]
  }
)

//This returns a Fault { message: "prop1 cannot be hello" }

Builder Predicates

Similar to Asserts, but returns a Skip instead of Fault.

export const input = {
  prop1: "hello"
}

export const schema = traverse(
  {
    prop1: capture(),
  },
  {
    builders: [{
      predicates: [{ predicate: (obj, context) => context.state.prop1 !== "hello", message: "prop1 cannot be hello" }],
      get: (obj, context) => ({ prop1: context.state.prop1 + " world" })
    }]
  }
)

//This returns a Skip { message: "prop1 cannot be hello" }