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Add lambda expression and map() + filter() functions with ARM syntax
#1238
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Add lambda expression and map() + filter() functions with ARM syntax
#1238
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Pull Request Overview
This PR implements lambda expressions and the map() function for DSC configuration documents, using ARM-compatible syntax (lambda('param', body) and lambdaVariables('param')). The implementation stores lambdas in the context with unique UUID-based identifiers and evaluates them by binding lambda parameters to array elements.
Key changes:
- Added
Lambdastruct and lambda-specific handling in the function evaluation pipeline - Implemented
map(),lambda(), andlambdaVariables()functions for array transformations - Extended
Contextwith lambda storage (lambdas) and lambda parameter bindings (lambda_variables)
Reviewed Changes
Copilot reviewed 8 out of 8 changed files in this pull request and generated 8 comments.
Show a summary per file
| File | Description |
|---|---|
| lib/dsc-lib/src/parser/functions.rs | Added Lambda struct and FunctionArg::Lambda variant; special handling for lambda() function to bypass normal evaluation |
| lib/dsc-lib/src/functions/mod.rs | Implemented invoke_lambda() to create and store lambda objects with UUID-based IDs; registered new lambda-related functions |
| lib/dsc-lib/src/functions/map.rs | Implemented array transformation function that evaluates lambdas for each element with optional index parameter |
| lib/dsc-lib/src/functions/lambda_variables.rs | Implemented parameter lookup function for accessing lambda-bound variables during evaluation |
| lib/dsc-lib/src/functions/lambda.rs | Created lambda function stub that returns error if invoked directly (handled specially elsewhere) |
| lib/dsc-lib/src/configure/context.rs | Added lambda_variables HashMap and lambdas RefCell for lambda storage and parameter binding |
| lib/dsc-lib/locales/en-us.toml | Added localized error messages and descriptions for lambda-related functions |
| dsc/tests/dsc_lambda.tests.ps1 | Added integration tests for map() with various lambda scenarios (multiplication, index usage, range, empty array) |
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…//github.com/Gijsreyn/operation-methods into PowerShellgh-57/main/add-map-lambda-function
lib/dsc-lib/src/functions/map.rs
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| for (index, element) in array.iter().enumerate() { | ||
| // Create a new context with lambda variables bound | ||
| let mut lambda_context = context.clone(); | ||
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| // Bind first parameter to array element | ||
| lambda_context.lambda_variables.insert( | ||
| lambda.parameters[0].clone(), | ||
| element.clone() | ||
| ); | ||
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| // Bind second parameter to index if provided | ||
| if lambda.parameters.len() == 2 { | ||
| lambda_context.lambda_variables.insert( | ||
| lambda.parameters[1].clone(), | ||
| Value::Number(serde_json::Number::from(index)) | ||
| ); | ||
| } | ||
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| // Evaluate lambda body with bound variables | ||
| let result = lambda.body.invoke(&dispatcher, &lambda_context)?; | ||
| result_array.push(result); | ||
| } |
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I haven't thought this through, but instead of having each lambda function implement processing lambdas, it would seem like this could be in lambda() itself so the other lambda functions in https://learn.microsoft.com/en-us/azure/azure-resource-manager/templates/template-functions-lambda would just handle how to apply the lambda result.
Perhaps it would help to also implement filter() in this PR to see how it would work?
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I added the filter() function to compare, where I had introduced a new file (lamba_helpers.rs). Mind checking again?
map() function with ARM syntaxmap() + filter() functions with ARM syntax
PR Summary
This PR implements lambda expressions and the
map()function for DSC configuration documents, enabling array transformations. The implementation uses ARM compatible syntax e.g., (lambda('param', body)andlambdaVariables('param'))Example usage:
Seperated tests in a different file.
PR Context
Partially addresses #57.