; var <- selectSimpleMatchVarL pat
; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
result_ty (cantFailMatchResult body)
; match_code <- handle_failure pat match fail_op
; var <- selectSimpleMatchVarL pat
; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat
result_ty (cantFailMatchResult body)
; match_code <- handle_failure pat match fail_op