A scanner (or lexer) takes in the linear stream of characters and chunks them together into a series of something more akin to “words”. In programming languages, each of these words is called a token
Parser
A parser takes the flat sequence of tokens and builds a tree structure that mirrors the nested nature of the grammar. These trees have a couple of different names—parse tree or abstract syntax tree—depending on how close to the bare syntactic structure of the source language they are. In practice, language hackers usually call them syntax trees, ASTs, or often just trees.
intermediate representation
There are a few well-established styles of IRs out there. Hit your search engine of choice and look for “control flow graph”, “static single-assignment”, “continuation-passing style”, and “three-address code”.
A shared intermediate representation reduces that dramatically. You write one front end for each source language that produces the IR. Then one back end for each target architecture. Now you can mix and match those to get every combination.
