Sema

A Lisp where LLM agents are language primitives, not an SDK — compiled to a fast bytecode VM, shipped as a single binary.

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Stop rewriting the agent loop. Every LLM script grows the same scaffolding — retries, caching, cost caps, rate limits, tool dispatch, conversation state. Sema makes that scaffolding the runtime: your script stays the size of its idea, ships as a single binary, and your coding agent already speaks the language.

Sema is a Scheme-like Lisp where prompts are s-expressions, conversations are persistent data structures, and LLM calls are just another form of evaluation — with Clojure-style keywords (:foo), map literals ({:key val}), and vector literals ([1 2 3]).

What It Looks Like

A coding agent with file tools, safety checks, and budget tracking — in ~40 lines:

;; Define tools the LLM can call
(deftool read-file
  "Read a file's contents"
  {:path {:type :string :description "File path"}}
  (lambda (path)
    (if (file/exists? path) (file/read path) "File not found")))

(deftool edit-file
  "Replace text in a file"
  {:path {:type :string} :old {:type :string} :new {:type :string}}
  (lambda (path old new)
    (file/write path (string/replace (file/read path) old new))
    "Done"))

(deftool run-command
  "Run a shell command"
  {:command {:type :string :description "Shell command to run"}}
  (lambda (command) (:stdout (shell "sh" "-c" command))))

;; Create an agent with tools, system prompt, and spending limit
(defagent coder
  {:system (format "You are a coding assistant. Working directory: ~a" (sys/cwd))
   :tools [read-file edit-file run-command]
   :max-turns 20})   ; no :model → uses the configured default provider

;; Run it — budget is scoped, automatically restored after the block
(llm/with-budget {:max-cost-usd 0.50} (lambda ()
  (define result (agent/run coder "Add error handling to src/main.rs"))
  (println (:response result))
  (println (format "Cost: $~a" (:spent (llm/budget-remaining))))))

Key Features

;; Simple completion
(llm/complete "Explain monads in one sentence")

;; Structured data extraction — returns a map, not a string
(llm/extract
  {:vendor {:type :string} :amount {:type :number} :date {:type :string}}
  "Bought coffee for $4.50 at Blue Bottle on Jan 15")
;; => {:amount 4.5 :date "2025-01-15" :vendor "Blue Bottle"}

;; Classification
(llm/classify (list :positive :negative :neutral) "This product is amazing!")
;; => :positive

;; Multi-turn conversations as immutable data
(define conv (conversation/new {:model "claude-haiku-4-5-20251001"}))
(define conv (conversation/say conv "The secret number is 7"))
(define conv (conversation/say conv "What's the secret number?"))
(conversation/last-reply conv) ;; => "The secret number is 7."

;; Streaming
(llm/stream "Tell me a story" {:max-tokens 500})

;; Batch — all prompts sent concurrently
(llm/batch (list "Translate 'hello' to French"
                 "Translate 'hello' to Spanish"
                 "Translate 'hello' to German"))