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diff --git a/lib/Language/Elna/Driver/CommandLine.hs b/lib/Language/Elna/Driver/CommandLine.hs
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+++ b/lib/Language/Elna/Driver/CommandLine.hs
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+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+module Language.Elna.Driver.CommandLine
+    ( CommandLine(..)
+    , IntermediateStage(..)
+    , commandLine
+    ) where
+
+import Options.Applicative
+    ( Parser
+    , ParserInfo(..)
+    , argument
+    , flag'
+    , fullDesc
+    , help
+    , helper
+    , info
+    , long
+    , metavar
+    , optional
+    , progDesc
+    , short
+    , str
+    , strOption
+    )
+import Control.Applicative (Alternative(..), (<**>))
+
+data IntermediateStage
+    = ParseStage
+    | ValidateStage
+    | CodeGenStage
+    deriving (Eq, Show)
+
+data CommandLine = CommandLine
+    { input :: FilePath
+    , output :: Maybe FilePath
+    , intermediateStage :: Maybe IntermediateStage
+    } deriving (Eq, Show)
+
+intermediateStageP :: Parser IntermediateStage
+intermediateStageP
+    = flag' ParseStage parseStageP
+    <|>  flag' ValidateStage validateStageP
+    <|> flag' CodeGenStage codeGenStageP
+  where
+    parseStageP = long "parse"
+        <> help "Run the lexer and parser, but stop before assembly generation"
+    validateStageP = long "validate"
+        <> help "Run through the semantic analysis stage, stopping before TAC generation"
+    codeGenStageP = long "codegen"
+        <> help "Perform lexing, parsing, and assembly generation, but stop before code emission"
+
+commandLineP :: Parser CommandLine
+commandLineP = CommandLine
+    <$> argument str inFile
+    <*> optional (strOption outFile)
+    <*> optional intermediateStageP
+  where
+    inFile = metavar "INFILE" <> help "Input file."
+    outFile = long "output"
+        <> short 'o'
+        <> metavar "OUTFILE"
+        <> help "Output file."
+
+commandLine :: ParserInfo CommandLine
+commandLine = info (commandLineP <**> helper)
+    $ fullDesc <> progDesc "Elna compiler."