Perform constant evaluation during constant declaration analysis

analyzer/type.go

@@ -1,6 +1,7 @@
 package analyzer
 
 import "fmt"
+import "git.tebibyte.media/fspl/fspl/eval"
 import "git.tebibyte.media/fspl/fspl/errors"
 import "git.tebibyte.media/fspl/fspl/entity"
 
@@ -101,11 +102,8 @@ func (this *Tree) analyzeConstantDeclaration (
 		value, err := this.analyzeExpression(into, strict, constant.Value)
 		if err != nil { return nil, err }
 
-		// TODO once constant expression evaluation is implemented, do
-		// that here
-		
-		// only allow values that can be used as constants
-		err = this.isConstant(value)
+		// evaluate constant expression to literal value
+		value, err = eval.EvaluateConstant(value)
 		if err != nil { return nil, err }
 	}