complete rewrite of gdt.lm using mini expr parser - gsl-shell.git - gsl-shell

diff --git a/expr-print.lua b/expr-print.lua
new file mode 100644
index 00000000..27e8f75c
--- /dev/null
+++ b/expr-print.lua

@@ -0,0 +1,52 @@

+local format, concat = string.format, table.concat

+

+local oper_table = {['+'] = 0, ['-'] = 0, ['*'] = 1, ['/'] = 1, ['^'] = 2}

+

+local ex_print

+

+local function is_ident_simple(s)

+ return s:match('^[%l%u_][%w_]*$')

+end

+

+local function op_print(e, prio)

+ if #e == 1 then

+ local c, c_prio = ex_print(e[1])

+ if c_prio < prio then c = format('(%s)', c) end

+ return format("%s%s", e.operator, c)

+ else

+ local a, a_prio = ex_print(e[1])

+ local b, b_prio = ex_print(e[2])

+ if a_prio < prio then a = format('(%s)', a) end

+ if b_prio < prio then b = format('(%s)', b) end

+ local temp = (prio < 2 and "%s %s %s" or "%s%s%s")

+ return format(temp, a, e.operator, b)

+ end

+end

+

+local function exlist_print(e)

+ local t = {}

+ for k = 1, #e do t[k] = ex_print(e[k]) end

+ return concat(t, ', ')

+end

+

+ex_print = function(e)

+ if type(e) == 'number' then

+ return e, 3

+ elseif type(e) == 'string' then

+ local s = e

+ if not is_ident_simple(s) then s = format('[%s]', s) end

+ return s, 3

+ else

+ local prio = oper_table[e.operator]

+ local s = op_print(e, prio)

+ return s, prio

+ end

+end

+

+local function schema_print(e)

+ local ys = exlist_print(e.y)

+ local xs = exlist_print(e.x)

+ return format("%s ~ %s", ys, xs)

+end

+

+return {schema = schema_print, expr = ex_print, expr_list = exlist_print}