DSL EXPRESSION:
$[FILENAME] = FNR


AST:
"block" [tt:block] [nt:StatementBlock]
    "=" [tt:equals] [nt:Assignment]
        "$[]" [tt:$[]] [nt:IndirectFieldValue]
            "FILENAME" [tt:ctx_FILENAME] [nt:ctx_FILENAME]
        "FNR" [tt:ctx_FNR] [nt:ctx_FNR]

