For AI agents: the complete documentation index is available at /hclapi/llms.txt, the full documentation bundle is available at /hclapi/llms-full.txt, and this page is available as Markdown at /hclapi/docs/concepts/expressions.md.
hclapi
    Install

    Expressions

    Request-time HCL expressions for context access, conditions, interpolation, argument mapping, and response construction.

    HCL attributes support expressions evaluated at request time. Expressions read from ctx to map parameters, branch on conditions, interpolate strings, and construct response bodies.

    Operators

    OperatorMeaningExample
    ==, !=Equalitysteps.lookup.rows_affected == 0
    >, >=, <, <=Numeric comparisonsteps.inventory.result.count < 5
    &&Logical ANDsteps.auth.result.valid == true && ctx.request.body.admin == true
    ||Logical ORctx.request.query.format == "csv" || ctx.request.query.format == "xlsx"
    !Logical NOT!steps.user.result.is_active

    A field that may be absent is compared against null:

    respond {
  condition = steps.cache_lookup.result != null
  status    = 200
  body      = steps.cache_lookup.result
}

    String interpolation

    ${...} substitutes values from ctx.request or steps.

    redis "session_write" {
  connection = connection.redis.sessions
  command    = "SET"

  key   = "session:${ctx.request.headers.x_session_id}:user"
  value = steps.find_user.result.id
  ttl   = "15m"
}

    Argument mapping

    args maps context values to parameterized query inputs. Parameters bound through @param in a sql block are sanitized automatically.

    sql "update_account" {
  connection = connection.postgres.main

  query = <<-SQL
    UPDATE accounts
    SET name = @name, updated_at = NOW()
    WHERE id = @id
    RETURNING id, name, updated_at
  SQL

  args = {
    id   = ctx.request.path.id
    name = steps.sanitize_input.result.clean_name
  }
}

    Response bodies

    Object and list literals can be constructed inline.

    respond {
  status = 201

  body = {
    account = steps.create_account.result

    metadata = {
      requested_by = ctx.request.headers.authorization
      created_at   = ctx.timestamp_epoch
      tags         = ["api", "v1", ctx.request.query.environment]
    }
  }
}