Language.Scheme.Core

This module contains Core functionality, primarily Scheme expression evaluation.

Scheme code evaluation

evalLisp :: Env -> LispVal -> IOThrowsError LispVal

Evaluate a lisp data structure and return a value for use by husk

evalLisp' :: Env -> LispVal -> IO (ThrowsError LispVal)

Evaluate a lisp data structure and return the LispVal or LispError result directly

 result <- evalLisp' env $ List [Atom "/", Number 1, Number 0]
 case result of
   Left err -> putStrLn $ "Error: " ++ (show err)
   Right val -> putStrLn $ show val

evalString :: Env -> String -> IO String

Evaluate a string containing Scheme code

env <- primitiveBindings

evalString env "(+ x x x)"
"3"

evalString env "(+ x x x (* 3 9))"
"30"

evalString env "(* 3 9)"
"27"

evalAndPrint :: Env -> String -> IO ()

Evaluate a string and print results to console

apply

Arguments

:: LispVal

Current continuation

-> LispVal

Function or continuation to execute

-> [LispVal]

Arguments

-> IOThrowsError LispVal

Final value of computation

Call into a Scheme function

continueEval

Arguments

:: Env

Current environment

-> LispVal

Current continuation

-> LispVal

Value of previous computation

-> Maybe [LispVal]

Extra arguments from previous computation

-> IOThrowsError LispVal

Final value of computation

A support function for eval; eval calls into this function instead of returning values directly. continueEval then uses the continuation argument to manage program control flow.

runIOThrows :: IOThrowsError String -> IO (Maybe String)

Execute an IO action and return error or Nothing if no error was thrown.

runIOThrowsREPL :: IOThrowsError String -> IO String

Execute an IO action and return result or an error message. This is intended for use by a REPL, where a result is always needed regardless of type.

Core data

nullEnvWithImport :: IO Env

An empty environment with the %import function. This is presently just intended for internal use by the compiler.

primitiveBindings :: IO Env

Environment containing the primitive forms that are built into the Scheme language. This function only includes forms that are implemented in Haskell; derived forms implemented in Scheme (such as let, list, etc) are available in the standard library which must be pulled into the environment using (load)

For the purposes of using husk as an extension language, r5rsEnv will probably be more useful.

r5rsEnv :: IO Env

Load the standard r5rs environment, including libraries

r5rsEnv' :: IO Env

Load the standard r5rs environment, including libraries, but do not create the (import) binding

r7rsEnv :: IO Env

Load the standard r7rs environment, including libraries

Note that the only difference between this and the r5rs equivalent is that slightly less Scheme code is loaded initially.

r7rsEnv' :: IO Env

Load the standard r7rs environment

r7rsTimeEnv :: IO Env

Load haskell bindings used for the r7rs time library

version :: String

Husk version number

Utility functions

findFileOrLib :: String -> ExceptT LispError IO String

Attempts to find the file both in the current directory and in the husk libraries. If the file is not found in the current directory but exists as a husk library, return the full path to the file in the library. Otherwise just return the given filename.

getDataFileFullPath :: String -> IO String

Get the full path to a data file installed for husk

replaceAtIndex :: forall a. Int -> a -> [a] -> [a]

Replace a list element, by index. Taken from: http://stackoverflow.com/questions/10133361/haskell-replace-element-in-list

registerExtensions :: Env -> (FilePath -> IO FilePath) -> IO ()

Register optional SRFI extensions

showBanner :: IO ()

A utility function to display the husk console banner

showLispError :: LispError -> IO String

This is the recommended function to use to display a lisp error, instead of just using show directly.

substr :: (LispVal, LispVal, LispVal) -> IOThrowsError LispVal

A helper function for the special form (string-set!)

updateList :: LispVal -> LispVal -> LispVal -> IOThrowsError LispVal

A helper function for (list-set!)

updateVector :: LispVal -> LispVal -> LispVal -> IOThrowsError LispVal

A helper function for the special form (vector-set!)

updateByteVector :: LispVal -> LispVal -> LispVal -> IOThrowsError LispVal

A helper function for the special form (bytevector-u8-set!)

hashTblRef :: [LispVal] -> IOThrowsError LispVal

Retrieve the value from the hashtable for the given key. An error is thrown if the key is not found.

Note this had to be made an EvalFunc because a thunk can be passed as an optional argument to be executed if the key is not found.

Arguments:

• Current continuation
• HashTable to copy
• Object that is the key to query the table for

Returns: Object containing the key's value

Error handling

addToCallHistory :: LispVal -> [LispVal] -> [LispVal]

Add a function to the call history

throwErrorWithCallHistory :: LispVal -> LispError -> IOThrowsError LispVal

Rethrow given error with call history, if available

Internal use only

meval :: Env -> LispVal -> LispVal -> IOThrowsError LispVal

A wrapper for macroEval and eval