feat(cli): add repl and file runner

src/Fml.Cli/Program.fs

@@ -0,0 +1,65 @@
+module Fml.Cli.Program
+
+open System
+open Fml.Core.Lexer
+open Fml.Core.Parser
+open Fml.Core.Types
+open Fml.Core.Match
+open Fml.Core.Value
+open Fml.Core.Interpreter
+
+let private printResult (r: PhraseResult) =
+    printfn "val %s : %s = %s" r.Name r.TypeText r.ValueText
+
+let private reportError (kind: string) (message: string) = eprintfn "%s: %s" kind message
+
+let private runFile (path: string) : int =
+    let source = IO.File.ReadAllText path
+    let session = Session()
+    session.LoadPrelude()
+    try
+        for phrase in parsePhrases source do
+            session.RunPhrase phrase |> List.iter printResult
+        0
+    with
+    | LexError m -> reportError "Lex error" m; 1
+    | ParseError m -> reportError "Parse error" m; 1
+    | TypeError m -> reportError "Type error" m; 1
+    | MatchError m -> reportError "Match error" m; 1
+    | RuntimeError m -> reportError "Runtime error" m; 1
+
+let private repl () =
+    printfn "fml REPL - enter an expression or a definition, Ctrl-D to quit."
+    let session = Session()
+    session.LoadPrelude()
+    let mutable running = true
+    while running do
+        Console.Out.Write "fml> "
+        Console.Out.Flush()
+        let line = Console.In.ReadLine()
+        if isNull line then
+            running <- false
+        elif line.Trim() = "" then
+            ()
+        else
+            try
+                for phrase in parsePhrases line do
+                    session.RunPhrase phrase |> List.iter printResult
+            with
+            | LexError m -> printfn "Lex error: %s" m
+            | ParseError m -> printfn "Parse error: %s" m
+            | TypeError m -> printfn "Type error: %s" m
+            | MatchError m -> printfn "Match error: %s" m
+            | RuntimeError m -> printfn "Runtime error: %s" m
+    printfn "bye"
+
+[<EntryPoint>]
+let main argv =
+    match argv with
+    | [||] ->
+        repl ()
+        0
+    | [| path |] -> runFile path
+    | _ ->
+        eprintfn "usage: fml [file.fml]"
+        1