# All files / src/core function.js

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     /* Core function plugin
     *
     * @flow
     *
     * This plugin only handles the basics of functions like vanilla function calls,
     * arguments and return statements
     */
    import Syntax from 'walt-syntax';
    import { current, enter, exit, signature } from 'walt-parser-tools/scope';
    import walkNode from 'walt-parser-tools/walk-node';
    import {
      FUNCTION_INDEX,
      FUNCTION_METADATA,
      LOCAL_INDEX,
    } from '../semantics/metadata';
    import { typeWeight } from '../types';
    import type {
      SemanticPlugin,
      FunctionDeclaration,
      FunctionArguments,
      Context,
    } from '../flow/types';

    export default function coreFunctionPlugin(): SemanticPlugin {
      return {
        semantics() {
          return {
            [Syntax.FunctionDeclaration]: _ignore => (
              [fun, context]: [FunctionDeclaration, Context],
              transform
            ) => {
              // Enter a new scope, where all new declaration will go into
              context.scopes = enter(context.scopes, LOCAL_INDEX);
              const currentScope = current(context.scopes);

              const [argsNode, resultNode, block] = fun.params;
              const [args, result] = [argsNode, resultNode].map(p =>
                transform([p, context])
              );

              const ref = {
                ...fun,
                // This is set by the parsers below if necessary, defaults to null
                type: currentScope[signature].result,
                meta: {
                  ...fun.meta,
                  [FUNCTION_INDEX]: Object.keys(context.functions).length,
                  [FUNCTION_METADATA]: {
                    argumentsCount: currentScope[signature].arguments.length,
                    locals: current(context.scopes),
                  },
                },
              };
              context.functions[fun.value] = ref;

              // Parse the block last, so that they can self-reference the function
              ref.params = [args, result, transform([block, context])];

              context.scopes = exit(context.scopes);

              return ref;
            },
            [Syntax.FunctionResult]: _next => ([result, context]) => {
              // Function statements are sybligs of FunctionResult so we need to mutate
              // the parent context (FunctionDeclaration)
              const currentScope = current(context.scopes);
              currentScope[signature].result = result.type;

              return result;
            },
            [Syntax.FunctionArguments]: _next => (
              [args, context]: [FunctionArguments, Context],
              transform
            ) => {
              const currentScope = current(context.scopes);

              currentScope[signature].arguments = [];

              walkNode({
                [Syntax.Pair]: node => {
                  const [identifier, typeNode] = node.params;

                  currentScope[signature].arguments.push(node);

                  transform([
                    {
                      ...node,
                      value: identifier.value,
                      type: typeNode.value,
                      params: [],
                      Type: Syntax.Declaration,
                    },
                    context,
                  ]);
                },
              })({ ...args, params: args.params.filter(Boolean) });

              return args;
            },
            // Regular function calls
            [Syntax.FunctionCall]: next => ([call, context]) => {
              const { functions } = context;
              const index = Object.keys(functions).indexOf(call.value);

              return next([
                {
                  ...call,
                  type:
                    functions[call.value] != null
                      ? functions[call.value].type
                      : null,
                  meta: { [FUNCTION_INDEX]: index },
                  params: call.params.slice(1),
                },
                context,
              ]);
            },
            [Syntax.ReturnStatement]: _next => (
              [returnNode, context],
              transform
            ) => {
              const currentScope = current(context.scopes);

              const [expression] = returnNode.params.map(p =>
                transform([p, context])
              );
              const { result } = currentScope[signature];
              // Constants as return values need to be assigned a correct type
              // (matching the result expected)
              if (
                expression != null &&
                expression.Type === Syntax.Constant &&
                typeWeight(expression.type) !== typeWeight(result)
              ) {
                return {
                  ...returnNode,
                  type: result,
                  params: [{ ...expression, type: result }],
                };
              }

              const type = expression ? expression.type : null;
              return {
                ...returnNode,
                params: [expression],
                type,
              };
            },
          };
        },
      };
    }