Fortran compilers did go through a phase when table-driven parsers were used, but it had the disadvantage of needing complicated lexers and statement classifier

Fortran compilers did go through a phase when table-driven parsers were used, but it had the disadvantage of needing complicated lexers and statement classifiers that rely on semantic information. Fortran’s a hard language to parse, given its lack of reserved words, optional spaces, and many ambiguities. The f18 compiler’s parser uses parser combinations to construct a backtracking recursive descent parser that builds a parse tree for the whole source file before doing any semantic analysis. This approach allows good error recovery without having to revert any updates to the symbol table.