LLM Engineering (7): Function Calling and Tool Use

Thu, 02 Apr 2026 09:00:00 +0000

Function calling connects an LLM to the world outside its weights. It combines chat-template details (Chapter 2 ), structured-output kernels (Chapter 5 ), and prompt engineering (Chapter 9 ). This chapter explores what happens under the hood, the guarantees you can rely on, and the agent-loop patterns that handle real workloads.

The intellectual lineage matters. Tool use as an LLM capability traces back to two near-simultaneous papers in 2022: MRKL Systems (Karpas et al., AI21) which proposed expert-routing among neuro-symbolic modules, and ReAct (Yao et al., 2022 ) which interleaved chain-of-thought reasoning with tool actions. Toolformer (Schick et al., 2023 ) showed self-supervised teaching of tool use, generating training data by having a model insert tool-call markers into existing text. By 2024 every frontier model had post-training data structured around the tool-use format, and tool calling moved from “research demo” to “API feature.”

Linux (9): Vim Essentials

Sat, 02 Apr 2022 10:00:00 +0000

Most people quit Vim because they try to memorize shortcuts. That’s the wrong approach. Vim is a small language: learn the grammar — operator + motion — and you can express any edit without ever opening a cheat sheet. This guide covers the 80% of Vim you’ll use daily and shows how the remaining 20% naturally follows from the same basic rules.

What You Will Learn#

The single core idea: modes plus composable operations (operator + motion)
The handful of motions, text objects, and operators that cover almost everything
File operations, search & replace, macros, marks, registers
Buffers vs windows vs tabs — the mental model people most often get wrong
A minimal .vimrc and a one-week deliberate-practice plan to build muscle memory

Prerequisites#

Any terminal (Vim ships with virtually every Unix-like system)
A willingness to feel slow for about a week

Tools on Chen Kai Blog

LLM Engineering (7): Function Calling and Tool Use

Linux (9): Vim Essentials

What You Will Learn#

Prerequisites#

The core idea — modes plus a tiny grammar#