cg/src/ast.ts

import type { Value } from './types';


// Literals and Variables

export type Literal = {
    kind: 'literal'
    value: Value
}

export type Variable = {
    kind: 'variable'
    name: string
}

export type Constructor = {
    kind: 'constructor'
    name: string
}

// Functions

export type Lambda = {
    kind: 'lambda'
    params: string[]
    body: AST
}

export type Apply = {
    kind: 'apply'
    func: AST
    args: AST[]
}

// Bindings

export type Let = {
    kind: 'let'
    name: string
    value: AST
    body: AST
}

// Matching

export type Match = {
    kind: 'match'
    expr: AST
    cases: MatchCase[]
}

export type MatchCase = {
    pattern: Pattern
    result: AST
}

export type Pattern =
    | { kind: 'wildcard' }
    | { kind: 'var', name: string }
    | { kind: 'literal', value: number | string }
    | { kind: 'constructor', name: string, args: Pattern[] }
    | { kind: 'list', elements: Pattern[] }
    | { kind: 'record', fields: { [key: string]: Pattern } }

// Data Structures

export type Record = {
    kind: 'record'
    fields: { [key: string]: AST }
}

export type RecordAccess = {
    kind: 'record-access'
    record: AST
    field: string
}

export type RecordUpdate = {
    kind: 'record-update'
    record: AST
    updates: { [key: string]: AST }
}

export type List = {
    kind: 'list'
    elements: AST[]
}

// Top-level constructs

export type Definition = {
    kind: 'definition'
    name: string
    body: AST
    // type?: string // TODO
}

export type TypeDef = {
    kind: 'typedef'
    name: string
    variants: Array<{ name: string, args: string[] }>
}

export type Import = {
    kind: 'import'
    module: string
    items: string[] | 'all'
}

export type AST =
    | Literal
    | Variable
    | Constructor
    | Lambda
    | Apply
    | Let
    | Match
    | Record
    | RecordAccess
    | RecordUpdate
    | List
    | Definition
    | TypeDef
    | Import

export function prettyPrint(ast: AST, indent = 0): string {
    const i = ' '.repeat(indent);

    switch (ast.kind) {
        case 'literal':
            return `${i}${ast.value.value}`;

        case 'variable':
            return `${i}${ast.name}`;

        case 'constructor':
            return `${i}${ast.name}`;

        case 'apply':
            const func = prettyPrint(ast.func, 0);
            const args = ast.args.map(a => prettyPrint(a, 0)).join(' ');
            return `${i}(${func} ${args})`

        case 'let':
            return `${i}let ${ast.name} = \n${prettyPrint(ast.value, indent + 1)}\n${i}in\n${prettyPrint(ast.body, indent + 1)}`

        case 'list':
            const elems = ast.elements.map(e => prettyPrint(e, 0)).join(', ');
            return `${i}[${elems}]`;

        case 'record':
            const fields = Object.entries(ast.fields)
                .map(([k, v]) => `${k} = ${prettyPrint(v, 0)}`)
                .join(', ');
            return `${i}{${fields}}`;

        case 'lambda':
            const params = ast.params.join(', ')
            return `${i}(${params}) => ${prettyPrint(ast.body)}`

        case 'record-access':
            return `${i}${prettyPrint(ast.record)}.${ast.field}`

        case 'record-update':
            const updates = Object.entries(ast.updates).map(([k, v]) => `${k} = ${prettyPrint(v, 0)}`).join(', ');
            return `${i}${prettyPrint(ast.record)} { ${updates} }`

        default:
            return `${i}${ast.kind}`
    }
}