Modify Transformer

Modifying a transformer follows the same builder pattern as modifying a parser, using IndirBuilder and IndirDef from @traqula/core as described in creating a transformer.

Modifying Indirection-Based Transformers

As with all builders, start by creating a copy of the builder you're extending:

import { IndirBuilder } from '@traqula/core';
const myTransformerBuilder = IndirBuilder.create(existingTransformerBuilder);
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The IndirBuilder exposes the following manipulation methods:

• getRule(name): Retrieve an existing definition for inspection or wrapping.
• patchRule(rule): Replace the implementation of an existing definition.
• addRule(rule): Add a new definition (TypeScript errors on name conflict).
• addMany(rule1, rule2, ...): Add multiple definitions at once.
• deleteRule(name) / deleteMany(...names): Remove definitions.
• typePatch<{...}>(): Update type signatures without changing implementations.
• widenContext(): Narrow the context type parameter to a more specific subtype.
• merge(otherBuilder, overrides): Merge with another IndirBuilder.

Example: Patching a Transformation Step

import type { IndirDef } from '@traqula/core';

// Retrieve the original for wrapping
const originalTranslate = existingBuilder.getRule('translateQuery');

// Create a replacement that handles additional AST node types
const extendedTranslate: IndirDef<MyContext, 'translateQuery', AlgebraOp, [QueryAST]> = {
  name: 'translateQuery',
  fun: ({ SUBRULE }) => (ctx, query) => {
    if (query.type === 'myCustomQuery') {
      return SUBRULE(translateMyCustomQuery, query);
    }
    // Fall back to the original for standard queries
    return originalTranslate.fun({ SUBRULE })(ctx, query);
  },
};

const myBuilder = IndirBuilder.create(existingBuilder)
  .addRule(translateMyCustomQuery)
  .patchRule(extendedTranslate);
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Modifying AST Tree Transformers

The AST tree transformers (TransformerObject, TransformerTyped, TransformerSubTyped) are not built through builders — they are instantiated directly with configuration. To modify their behavior, use the clone() method with new defaults:

// TransformerObject.clone() takes only a TransformContext:
const simpleTransformer = existingObjectTransformer.clone(
  { ignoreKeys: new Set(['metadata']) },
);

// TransformerTyped and TransformerSubTyped additionally accept
// default node-type pre-visitors as a second argument:
const typedTransformer = existingSubTypedTransformer.clone(
  // New default TransformContext
  { ignoreKeys: new Set(['metadata']) },
  // New default pre-visitors per node type (TransformerTyped/SubTyped only)
  { 'pattern': { continue: false } },
);
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For details on how to use these transformers, see the AST structure docs.