How was the first assembler assembled?

If we have the following things:

a) Monitor

b) A rudimentary file system

c) Shell

d) Keyboard input

e) Rudimentary text/line editor

Then the first, or one of the first "assemblers" that would have been written is HEX2BIN.

That is, you enter your assembly code, in hex, and you run HEX2BIN to generate your executable file.

All it does is convert hexadecimal character pairs 00-FF to a single binary value from 0-255, and writes that value to the standard output stream, which is hopefully redirected to the executable file to be generated.

That's it.

But that's a huge jump in functionality from using switches or even punched cards.

How does HEX2BIN evolve from there, what's its next step in becoming a more powerful assembler?

Labels.

That is, the abililty to insert a text label into the HEX stream, which will now represent an address after the code preceding it is converted, and the ability for the fledgling assembler to automatically insert that address in later code when it sees the text pattern of a label.

Newlines might be included in this "fledgling" assembler, that is, every line now can be either a hex stream, OR a label, and if it's a label, then further references to that label get auto converted to an address...

And the assembler evolves from there...