Fable
A set of instructions that can be called
In the old kitchen there were two kinds of work. Chopping vegetables, weighing salt, and lighting the fire all had fixed methods; writing banquet menus, however, relied on the head chef explaining it verbally to apprentices. Doing the two kinds of work separately could barely get dishes out.
Later the banquets grew more and more complex. The accounts office wanted to connect menu generation to the order form, the front hall wanted to connect guest tastes to the recipe book, but the kitchen could only say: have the head chef explain it again.
Someone copied the chef's words onto a whole page and pasted it on the wall. Every time the taste, number of people, or budget needed to change, the apprentice manually edited a few sentences. The more the notes were edited, the messier they became, and no one knew which sentence was a variable and which was a rule.
Then someone wrote all the menus as hard code. This was stable, but it lost the flexibility of language. When customers said less oil, avoid spice, suitable for the elderly, the code table quickly expanded.
The new steward put the passage the chef often recited into a small wooden box. The box had a name and input fields: number of people, budget, dietary restrictions, cuisine. Give it these things, and it generates a menu according to that passage.
Beside it were ordinary toolboxes that could check inventory, calculate costs, and print purchase orders. The steward lined up the two kinds of boxes: first use the language box to produce a plan, then use the ordinary toolboxes to validate and execute.
The apprentice discovered that language was no longer just a prompt stuck on the wall, nor a special case hidden in the code. It had become a kitchen capability that could be invoked, composed and reused.
The steward still restricted the uses of the boxes. The menu box could not directly place purchase orders, and the purchasing box could not arbitrarily change customers' tastes. Each box had clear inputs, outputs, and boundaries. The head chef said: when a piece of natural-language instruction can be named, passed parameters, and composed like a function, it turns from oral experience into a system component. Later the kitchen made another banquet rewriting box. The front hall gave it customer preferences, and it produced only menu suggestions; the accounting office gave the purchasing box a budget, and it calculated only costs. The steward did not allow the two boxes to cross boundaries, because once the menu box could directly buy groceries, one wrong sentence would become a cartload of wrong goods. The kitchen thus preserved the flexibility of language while giving each instruction a fixed entry point, exit point, and scope of responsibility. Later the apprentice wrote example inputs and error outputs for each box. When a new chef took over, they did not have to guess the head chef's tone to know how that instruction should be used. Being callable also means being constrainable.