Initial import of Fantomas client library (#6)

WoofWare.Whippet.Fantomas/SynMatchClause.fs

@@ -0,0 +1,28 @@
+namespace WoofWare.Whippet.Fantomas
+
+open Fantomas.FCS.Syntax
+open Fantomas.FCS.Text.Range
+
+/// Methods for manipulating SynMatchClause, a type representing a single arm of a `match` pattern match.
+/// For example, the entire line of code `| Foo (a, b) -> bar` is represented by one of these.
+[<RequireQualifiedAccess>]
+module SynMatchClause =
+    /// Represents the `match` arm `| {lhs} -> {rhs}`.
+    let create (lhs : SynPat) (rhs : SynExpr) : SynMatchClause =
+        SynMatchClause.SynMatchClause (
+            lhs,
+            None,
+            rhs,
+            range0,
+            DebugPointAtTarget.Yes,
+            {
+                ArrowRange = Some range0
+                BarRange = Some range0
+            }
+        )
+
+    /// Replace the `where` clause (or add a new one, if there isn't one already) in this `match` arm.
+    let withWhere (where : SynExpr) (m : SynMatchClause) : SynMatchClause =
+        match m with
+        | SynMatchClause (synPat, _, resultExpr, range, debugPointAtTarget, synMatchClauseTrivia) ->
+            SynMatchClause (synPat, Some where, resultExpr, range, debugPointAtTarget, synMatchClauseTrivia)