Create LintRule definition and simple implementation

Lint.elm

@@ -0,0 +1,114 @@
+module Lint exposing (lint, LintRule, Error)
+
+import Ast.Expression exposing (..)
+import Ast.Statement exposing (..)
+
+
+type alias Error =
+    String
+
+
+type alias LintImplementation nodeType context =
+    context -> nodeType -> ( List Error, context )
+
+
+type alias LintRule context =
+    { statementFn : LintImplementation Statement context
+    , typeFn : LintImplementation Type context
+    , expressionFn : LintImplementation Expression context
+    , context : context
+    }
+
+
+type alias Visitor context =
+    LintRule context -> context -> ( List Error, context )
+
+
+visitExpression : Expression -> Visitor context
+visitExpression node rule context =
+    rule.expressionFn context node
+
+
+visitType : Type -> Visitor context
+visitType node rule context =
+    rule.typeFn context node
+
+
+visitStatement : Statement -> Visitor context
+visitStatement node rule context =
+    rule.statementFn context node
+
+
+transformExpression : Expression -> List (Visitor context)
+transformExpression node =
+    let
+        visitAndTransformChildren children =
+            List.concat
+                [ [ visitExpression node ]
+                , List.concatMap transformExpression children
+                ]
+    in
+        case node of
+            Application expression1 expression2 ->
+                visitAndTransformChildren [ expression1, expression2 ]
+
+            Access expression names ->
+                visitAndTransformChildren [ expression ]
+
+            Variable _ ->
+                [ visitExpression node ]
+
+            _ ->
+                []
+
+
+transformType : Type -> List (Visitor context)
+transformType node =
+    []
+
+
+transformStatement : Statement -> List (Visitor context)
+transformStatement node =
+    let
+        visitAndTransformChildren expresssions types =
+            List.concat
+                [ [ visitStatement node ]
+                , List.concatMap transformExpression expresssions
+                , List.concatMap transformType types
+                ]
+    in
+        case node of
+            FunctionTypeDeclaration name application ->
+                visitAndTransformChildren [] [ application ]
+
+            FunctionDeclaration name params body ->
+                visitAndTransformChildren [ body ] []
+
+            _ ->
+                []
+
+
+transform : List Statement -> List (Visitor context)
+transform statements =
+    List.concatMap transformStatement statements
+
+
+lint : List Statement -> LintRule context -> List Error
+lint statements rule =
+    let
+        validators =
+            transform statements
+
+        ( errors, _ ) =
+            List.foldl
+                (\visitor ( errors, ctx ) ->
+                    let
+                        ( errors_, ctx_ ) =
+                            visitor rule ctx
+                    in
+                        ( errors ++ errors_, ctx_ )
+                )
+                ( [], rule.context )
+                validators
+    in
+        errors