# All files / src/generator if-then-else.js

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     // @flow
    import mapSyntax from "./map-syntax";
    import mergeBlock from "./merge-block";
    import opcode from "../emitter/opcode";
    import type { GeneratorType } from "./flow/types";

    // probably should be called "generateBranch" and be more generic
    // like handling ternary for example. A lot of shared logic here & ternary
    const generateIf: GeneratorType = (node, parent) => {
      const mapper = mapSyntax(parent);
      const [condition, thenBlock, ...restParams] = node.params;
      return [
        ...[condition].map(mapper).reduce(mergeBlock, []),
        {
          kind: opcode.If,
          // if-then-else blocks have no return value and the Wasm spec requires us to
          // provide a literal byte '0x40' for "empty block" in these cases
          params: [0x40],
        },

        // after the expression is on the stack and opcode is following it we can write the
        // implicit 'then' block
        ...[thenBlock].map(mapper).reduce(mergeBlock, []),

        // fllowed by the optional 'else'
        ...restParams.map(mapper).reduce(mergeBlock, []),
        { kind: opcode.End, params: [] },
      ];
    };

    export default generateIf;