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tm_tree Function ​

tm_tree converts an unordered list of parent-child pairs into hierarchical paths. It takes a list of [parent, child] tuples and returns a list of paths, where each path is a list of strings from root to node.

hcl
tm_tree(pairs)

The function processes parent-child relationships to build tree structures, where:

  • A null parent indicates a root node
  • Each path represents a complete branch from root to node
  • Output is deterministically sorted in lexicographical order

Arguments ​

  • pairs - A list of tuples, where each tuple contains [parent, child]. The parent can be null to indicate a root node.

Return Value ​

Returns a list of paths, where each path is a list of strings representing the hierarchical path from root to node.

Examples ​

Basic Tree Structure ​

hcl
locals {
  pairs = [
    [null, "root"],
    ["root", "child1"],
    ["root", "child2"],
    ["child1", "grandchild"]
  ]
  branches = tm_tree(local.pairs)
  # Returns: [
  #   ["root"],
  #   ["root", "child1"],
  #   ["root", "child1", "grandchild"],
  #   ["root", "child2"]
  # ]
}

Multiple Root Nodes ​

hcl
locals {
  pairs = [
    [null, "root1"],
    [null, "root2"],
    ["root1", "branch1"],
    ["root2", "branch2"]
  ]
  branches = tm_tree(local.pairs)
  # Returns: [
  #   ["root1"],
  #   ["root1", "branch1"],
  #   ["root2"],
  #   ["root2", "branch2"]
  # ]
}

Complex Hierarchies ​

hcl
locals {
  org_structure = [
    [null, "company"],
    ["company", "engineering"],
    ["company", "sales"],
    ["engineering", "backend"],
    ["engineering", "frontend"],
    ["backend", "api"],
    ["backend", "database"],
    ["frontend", "web"],
    ["frontend", "mobile"]
  ]
  org_tree = tm_tree(local.org_structure)
  # Returns hierarchical paths for the entire organization structure
}

Error Handling ​

The function validates the tree structure and will report errors for:

  • Cycles: When a node is its own ancestor
  • Conflicting Parents: When a child has multiple different parents
  • Unknown Parents: When a parent reference doesn't exist in the tree

Common Use Cases ​

Directory Structure Generation ​

hcl
locals {
  module_hierarchy = [
    [null, "modules"],
    ["modules", "networking"],
    ["modules", "compute"],
    ["networking", "vpc"],
    ["networking", "firewall"],
    ["compute", "instances"],
    ["compute", "loadbalancer"]
  ]
  module_paths = tm_tree(local.module_hierarchy)
  # Use with tm_joinlist to create file paths
  file_paths = tm_joinlist("/", local.module_paths)
}

Dependency Management ​

hcl
locals {
  dependencies = [
    [null, "base"],
    ["base", "network"],
    ["network", "compute"],
    ["compute", "application"]
  ]
  deployment_order = tm_tree(local.dependencies)
  # Returns deployment order respecting dependencies
}
  • tm_joinlist - Joins the hierarchical paths produced by tm_tree into string paths with a specified separator