Lambda the Ultimate

Has there been any PL research into languages where every semantically distinct program has exactly one representation in the source language? In other words, a language where for any given set of inputs, any change in the source text will create a program that for the same set of input produces a different set of outputs than the original program. Basically taking Python's "there should be one-- and preferably only one --obvious way to do it" philosophy to its logical extreme. I'm interested in how limiting this is on what you can express, since for any two equivalent algorithms only one of them could be written in the language. Is there an established technical term for this I can Google?