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Odd module variable assignment behavior

CS
Chris Spencer
Sun, Aug 30, 2015 10:33 PM

I ran into something very strange when tracking down an "undefined"
variable bug in my code. It turned out to be caused by the order in which I
declared my initial variables, and changing this order unintuitively causes
later reassignments to fail.

For example, consider this minimum reproducible example:

module test()
{
a = 1;
b = 2;
c = 3;
c = a + b;
echo("a:", a);
echo("b:", b);
echo("c:", c);
}

Running test() outputs the expected:

ECHO: "a:", 1
ECHO: "b:", 2
ECHO: "c:", 3

However, if you flip the ordering of the variables, reassignment fails:

module test()
{
a = 1;
c = 3;
b = 2;
c = a + b;
echo("a:", a);
echo("b:", b);
echo("c:", c);
}

So that running test() outputs the unexpected:

WARNING: Ignoring unknown variable 'b'.
ECHO: "a:", 1
ECHO: "b:", 2
ECHO: "c:", undef

Is this a bug? If it was simply a problem with the repeated assignment to
c, I would have expected each example to produce "undef".

My build info:

OpenSCAD Version: 2014.03

Compiler, build date: GCC "4.7.2", Mar 9 2014

Boost version: 1_53

Eigen version: 3.1.1

CGAL version, kernels: 4.0.2, Cartesian<Gmpq>, Extended_cartesian<Gmpq>,
Epeck

OpenCSG version: OpenCSG 1.3.2

Qt version: 4.8.2

MingW build: No

GLib version: 2.38.2

OPENSCADPATH: <not set>

OpenSCAD library path:

/home/chris/.local/share/OpenSCAD/libraries

/usr/local/lib/openscad/../../share/openscad/libraries

GLEW version: 1.9.0

OpenGL Version: 3.3.0 NVIDIA 340.76

GL Renderer: GeForce 9400M/integrated/SSE2

GL Vendor: NVIDIA Corporation

RGBA(8880), depth(24), stencil(8)

GL_ARB_framebuffer_object: yes

GL_EXT_framebuffer_object: yes

GL_EXT_packed_depth_stencil: yes

Using QGLWidget

GL Extensions:

GL_ARB_ES2_compatibility

GL_ARB_ES3_compatibility

GL_ARB_arrays_of_arrays

GL_ARB_base_instance

GL_ARB_blend_func_extended

GL_ARB_clear_buffer_object

GL_ARB_color_buffer_float

GL_ARB_compatibility

GL_ARB_compressed_texture_pixel_storage

GL_ARB_conservative_depth

GL_ARB_copy_buffer

GL_ARB_copy_image

GL_ARB_debug_output

GL_ARB_depth_buffer_float

GL_ARB_depth_clamp

GL_ARB_depth_texture

GL_ARB_draw_buffers

GL_ARB_draw_elements_base_vertex

GL_ARB_draw_instanced

GL_ARB_enhanced_layouts

GL_ARB_explicit_attrib_location

GL_ARB_explicit_uniform_location

GL_ARB_fragment_coord_conventions

GL_ARB_fragment_layer_viewport

GL_ARB_fragment_program

GL_ARB_fragment_program_shadow

GL_ARB_fragment_shader

GL_ARB_framebuffer_no_attachments

GL_ARB_framebuffer_object

GL_ARB_framebuffer_sRGB

GL_ARB_geometry_shader4

GL_ARB_get_program_binary

GL_ARB_half_float_pixel

GL_ARB_half_float_vertex

GL_ARB_imaging

GL_ARB_instanced_arrays

GL_ARB_internalformat_query

GL_ARB_internalformat_query2

GL_ARB_invalidate_subdata

GL_ARB_map_buffer_alignment

GL_ARB_map_buffer_range

GL_ARB_multi_bind

GL_ARB_multisample

GL_ARB_multitexture

GL_ARB_occlusion_query

GL_ARB_occlusion_query2

GL_ARB_pixel_buffer_object

GL_ARB_point_parameters

GL_ARB_point_sprite

GL_ARB_program_interface_query

GL_ARB_provoking_vertex

GL_ARB_robust_buffer_access_behavior

GL_ARB_robustness

GL_ARB_sampler_objects

GL_ARB_seamless_cube_map

GL_ARB_separate_shader_objects

GL_ARB_shader_bit_encoding

GL_ARB_shader_objects

GL_ARB_shader_texture_lod

GL_ARB_shading_language_100

GL_ARB_shading_language_420pack

GL_ARB_shading_language_include

GL_ARB_shading_language_packing

GL_ARB_shadow

GL_ARB_stencil_texturing

GL_ARB_sync

GL_ARB_texture_border_clamp

GL_ARB_texture_buffer_object

GL_ARB_texture_buffer_range

GL_ARB_texture_compression

GL_ARB_texture_compression_rgtc

GL_ARB_texture_cube_map

GL_ARB_texture_env_add

GL_ARB_texture_env_combine

GL_ARB_texture_env_crossbar

GL_ARB_texture_env_dot3

GL_ARB_texture_float

GL_ARB_texture_mirror_clamp_to_edge

GL_ARB_texture_mirrored_repeat

GL_ARB_texture_multisample

GL_ARB_texture_non_power_of_two

GL_ARB_texture_query_levels

GL_ARB_texture_rectangle

GL_ARB_texture_rg

GL_ARB_texture_rgb10_a2ui

GL_ARB_texture_stencil8

GL_ARB_texture_storage

GL_ARB_texture_storage_multisample

GL_ARB_texture_swizzle

GL_ARB_texture_view

GL_ARB_timer_query

GL_ARB_transform_feedback2

GL_ARB_transform_feedback_instanced

GL_ARB_transpose_matrix

GL_ARB_uniform_buffer_object

GL_ARB_vertex_array_bgra

GL_ARB_vertex_array_object

GL_ARB_vertex_attrib_binding

GL_ARB_vertex_buffer_object

GL_ARB_vertex_program

GL_ARB_vertex_shader

GL_ARB_vertex_type_10f_11f_11f_rev

GL_ARB_vertex_type_2_10_10_10_rev

GL_ARB_viewport_array

GL_ARB_window_pos

GL_ATI_draw_buffers

GL_ATI_texture_float

GL_ATI_texture_mirror_once

GL_EXTX_framebuffer_mixed_formats

GL_EXT_Cg_shader

GL_EXT_abgr

GL_EXT_bgra

GL_EXT_bindable_uniform

GL_EXT_blend_color

GL_EXT_blend_equation_separate

GL_EXT_blend_func_separate

GL_EXT_blend_minmax

GL_EXT_blend_subtract

GL_EXT_compiled_vertex_array

GL_EXT_depth_bounds_test

GL_EXT_direct_state_access

GL_EXT_draw_buffers2

GL_EXT_draw_instanced

GL_EXT_draw_range_elements

GL_EXT_fog_coord

GL_EXT_framebuffer_blit

GL_EXT_framebuffer_multisample

GL_EXT_framebuffer_multisample_blit_scaled

GL_EXT_framebuffer_object

GL_EXT_framebuffer_sRGB

GL_EXT_geometry_shader4

GL_EXT_gpu_program_parameters

GL_EXT_gpu_shader4

GL_EXT_import_sync_object

GL_EXT_multi_draw_arrays

GL_EXT_packed_depth_stencil

GL_EXT_packed_float

GL_EXT_packed_pixels

GL_EXT_pixel_buffer_object

GL_EXT_point_parameters

GL_EXT_provoking_vertex

GL_EXT_rescale_normal

GL_EXT_secondary_color

GL_EXT_separate_shader_objects

GL_EXT_separate_specular_color

GL_EXT_shader_integer_mix

GL_EXT_shadow_funcs

GL_EXT_stencil_two_side

GL_EXT_stencil_wrap

GL_EXT_texture3D

GL_EXT_texture_array

GL_EXT_texture_buffer_object

GL_EXT_texture_compression_dxt1

GL_EXT_texture_compression_latc

GL_EXT_texture_compression_rgtc

GL_EXT_texture_compression_s3tc

GL_EXT_texture_cube_map

GL_EXT_texture_edge_clamp

GL_EXT_texture_env_add

GL_EXT_texture_env_combine

GL_EXT_texture_env_dot3

GL_EXT_texture_filter_anisotropic

GL_EXT_texture_integer

GL_EXT_texture_lod

GL_EXT_texture_lod_bias

GL_EXT_texture_mirror_clamp

GL_EXT_texture_object

GL_EXT_texture_sRGB

GL_EXT_texture_sRGB_decode

GL_EXT_texture_shared_exponent

GL_EXT_texture_storage

GL_EXT_texture_swizzle

GL_EXT_timer_query

GL_EXT_transform_feedback2

GL_EXT_vertex_array

GL_EXT_vertex_array_bgra

GL_EXT_x11_sync_object

GL_IBM_rasterpos_clip

GL_IBM_texture_mirrored_repeat

GL_KHR_debug

GL_KTX_buffer_region

GL_NVX_conditional_render

GL_NVX_gpu_memory_info

GL_NV_ES1_1_compatibility

GL_NV_blend_square

GL_NV_conditional_render

GL_NV_copy_depth_to_color

GL_NV_copy_image

GL_NV_depth_buffer_float

GL_NV_depth_clamp

GL_NV_explicit_multisample

GL_NV_fence

GL_NV_float_buffer

GL_NV_fog_distance

GL_NV_fragment_program

GL_NV_fragment_program2

GL_NV_fragment_program_option

GL_NV_framebuffer_multisample_coverage

GL_NV_geometry_shader4

GL_NV_gpu_program4

GL_NV_half_float

GL_NV_light_max_exponent

GL_NV_multisample_coverage

GL_NV_multisample_filter_hint

GL_NV_occlusion_query

GL_NV_packed_depth_stencil

GL_NV_parameter_buffer_object

GL_NV_parameter_buffer_object2

GL_NV_path_rendering

GL_NV_pixel_data_range

GL_NV_point_sprite

GL_NV_primitive_restart

GL_NV_register_combiners

GL_NV_register_combiners2

GL_NV_shader_buffer_load

GL_NV_texgen_reflection

GL_NV_texture_barrier

GL_NV_texture_compression_vtc

GL_NV_texture_env_combine4

GL_NV_texture_expand_normal

GL_NV_texture_multisample

GL_NV_texture_rectangle

GL_NV_texture_shader

GL_NV_texture_shader2

GL_NV_texture_shader3

GL_NV_transform_feedback

GL_NV_transform_feedback2

GL_NV_vdpau_interop

GL_NV_vertex_array_range

GL_NV_vertex_array_range2

GL_NV_vertex_buffer_unified_memory

GL_NV_vertex_program

GL_NV_vertex_program1_1

GL_NV_vertex_program2

GL_NV_vertex_program2_option

GL_NV_vertex_program3

GL_S3_s3tc

GL_SGIS_generate_mipmap

GL_SGIS_texture_lod

GL_SGIX_depth_texture

GL_SGIX_shadow

GL_SUN_slice_accum

I ran into something very strange when tracking down an "undefined" variable bug in my code. It turned out to be caused by the order in which I declared my initial variables, and changing this order unintuitively causes later reassignments to fail. For example, consider this minimum reproducible example: module test() { a = 1; b = 2; c = 3; c = a + b; echo("a:", a); echo("b:", b); echo("c:", c); } Running test() outputs the expected: ECHO: "a:", 1 ECHO: "b:", 2 ECHO: "c:", 3 However, if you flip the ordering of the variables, reassignment fails: module test() { a = 1; c = 3; b = 2; c = a + b; echo("a:", a); echo("b:", b); echo("c:", c); } So that running test() outputs the unexpected: WARNING: Ignoring unknown variable 'b'. ECHO: "a:", 1 ECHO: "b:", 2 ECHO: "c:", undef Is this a bug? If it was simply a problem with the repeated assignment to c, I would have expected each example to produce "undef". My build info: OpenSCAD Version: 2014.03 Compiler, build date: GCC "4.7.2", Mar 9 2014 Boost version: 1_53 Eigen version: 3.1.1 CGAL version, kernels: 4.0.2, Cartesian<Gmpq>, Extended_cartesian<Gmpq>, Epeck OpenCSG version: OpenCSG 1.3.2 Qt version: 4.8.2 MingW build: No GLib version: 2.38.2 OPENSCADPATH: <not set> OpenSCAD library path: /home/chris/.local/share/OpenSCAD/libraries /usr/local/lib/openscad/../../share/openscad/libraries GLEW version: 1.9.0 OpenGL Version: 3.3.0 NVIDIA 340.76 GL Renderer: GeForce 9400M/integrated/SSE2 GL Vendor: NVIDIA Corporation RGBA(8880), depth(24), stencil(8) GL_ARB_framebuffer_object: yes GL_EXT_framebuffer_object: yes GL_EXT_packed_depth_stencil: yes Using QGLWidget GL Extensions: GL_ARB_ES2_compatibility GL_ARB_ES3_compatibility GL_ARB_arrays_of_arrays GL_ARB_base_instance GL_ARB_blend_func_extended GL_ARB_clear_buffer_object GL_ARB_color_buffer_float GL_ARB_compatibility GL_ARB_compressed_texture_pixel_storage GL_ARB_conservative_depth GL_ARB_copy_buffer GL_ARB_copy_image GL_ARB_debug_output GL_ARB_depth_buffer_float GL_ARB_depth_clamp GL_ARB_depth_texture GL_ARB_draw_buffers GL_ARB_draw_elements_base_vertex GL_ARB_draw_instanced GL_ARB_enhanced_layouts GL_ARB_explicit_attrib_location GL_ARB_explicit_uniform_location GL_ARB_fragment_coord_conventions GL_ARB_fragment_layer_viewport GL_ARB_fragment_program GL_ARB_fragment_program_shadow GL_ARB_fragment_shader GL_ARB_framebuffer_no_attachments GL_ARB_framebuffer_object GL_ARB_framebuffer_sRGB GL_ARB_geometry_shader4 GL_ARB_get_program_binary GL_ARB_half_float_pixel GL_ARB_half_float_vertex GL_ARB_imaging GL_ARB_instanced_arrays GL_ARB_internalformat_query GL_ARB_internalformat_query2 GL_ARB_invalidate_subdata GL_ARB_map_buffer_alignment GL_ARB_map_buffer_range GL_ARB_multi_bind GL_ARB_multisample GL_ARB_multitexture GL_ARB_occlusion_query GL_ARB_occlusion_query2 GL_ARB_pixel_buffer_object GL_ARB_point_parameters GL_ARB_point_sprite GL_ARB_program_interface_query GL_ARB_provoking_vertex GL_ARB_robust_buffer_access_behavior GL_ARB_robustness GL_ARB_sampler_objects GL_ARB_seamless_cube_map GL_ARB_separate_shader_objects GL_ARB_shader_bit_encoding GL_ARB_shader_objects GL_ARB_shader_texture_lod GL_ARB_shading_language_100 GL_ARB_shading_language_420pack GL_ARB_shading_language_include GL_ARB_shading_language_packing GL_ARB_shadow GL_ARB_stencil_texturing GL_ARB_sync GL_ARB_texture_border_clamp GL_ARB_texture_buffer_object GL_ARB_texture_buffer_range GL_ARB_texture_compression GL_ARB_texture_compression_rgtc GL_ARB_texture_cube_map GL_ARB_texture_env_add GL_ARB_texture_env_combine GL_ARB_texture_env_crossbar GL_ARB_texture_env_dot3 GL_ARB_texture_float GL_ARB_texture_mirror_clamp_to_edge GL_ARB_texture_mirrored_repeat GL_ARB_texture_multisample GL_ARB_texture_non_power_of_two GL_ARB_texture_query_levels GL_ARB_texture_rectangle GL_ARB_texture_rg GL_ARB_texture_rgb10_a2ui GL_ARB_texture_stencil8 GL_ARB_texture_storage GL_ARB_texture_storage_multisample GL_ARB_texture_swizzle GL_ARB_texture_view GL_ARB_timer_query GL_ARB_transform_feedback2 GL_ARB_transform_feedback_instanced GL_ARB_transpose_matrix GL_ARB_uniform_buffer_object GL_ARB_vertex_array_bgra GL_ARB_vertex_array_object GL_ARB_vertex_attrib_binding GL_ARB_vertex_buffer_object GL_ARB_vertex_program GL_ARB_vertex_shader GL_ARB_vertex_type_10f_11f_11f_rev GL_ARB_vertex_type_2_10_10_10_rev GL_ARB_viewport_array GL_ARB_window_pos GL_ATI_draw_buffers GL_ATI_texture_float GL_ATI_texture_mirror_once GL_EXTX_framebuffer_mixed_formats GL_EXT_Cg_shader GL_EXT_abgr GL_EXT_bgra GL_EXT_bindable_uniform GL_EXT_blend_color GL_EXT_blend_equation_separate GL_EXT_blend_func_separate GL_EXT_blend_minmax GL_EXT_blend_subtract GL_EXT_compiled_vertex_array GL_EXT_depth_bounds_test GL_EXT_direct_state_access GL_EXT_draw_buffers2 GL_EXT_draw_instanced GL_EXT_draw_range_elements GL_EXT_fog_coord GL_EXT_framebuffer_blit GL_EXT_framebuffer_multisample GL_EXT_framebuffer_multisample_blit_scaled GL_EXT_framebuffer_object GL_EXT_framebuffer_sRGB GL_EXT_geometry_shader4 GL_EXT_gpu_program_parameters GL_EXT_gpu_shader4 GL_EXT_import_sync_object GL_EXT_multi_draw_arrays GL_EXT_packed_depth_stencil GL_EXT_packed_float GL_EXT_packed_pixels GL_EXT_pixel_buffer_object GL_EXT_point_parameters GL_EXT_provoking_vertex GL_EXT_rescale_normal GL_EXT_secondary_color GL_EXT_separate_shader_objects GL_EXT_separate_specular_color GL_EXT_shader_integer_mix GL_EXT_shadow_funcs GL_EXT_stencil_two_side GL_EXT_stencil_wrap GL_EXT_texture3D GL_EXT_texture_array GL_EXT_texture_buffer_object GL_EXT_texture_compression_dxt1 GL_EXT_texture_compression_latc GL_EXT_texture_compression_rgtc GL_EXT_texture_compression_s3tc GL_EXT_texture_cube_map GL_EXT_texture_edge_clamp GL_EXT_texture_env_add GL_EXT_texture_env_combine GL_EXT_texture_env_dot3 GL_EXT_texture_filter_anisotropic GL_EXT_texture_integer GL_EXT_texture_lod GL_EXT_texture_lod_bias GL_EXT_texture_mirror_clamp GL_EXT_texture_object GL_EXT_texture_sRGB GL_EXT_texture_sRGB_decode GL_EXT_texture_shared_exponent GL_EXT_texture_storage GL_EXT_texture_swizzle GL_EXT_timer_query GL_EXT_transform_feedback2 GL_EXT_vertex_array GL_EXT_vertex_array_bgra GL_EXT_x11_sync_object GL_IBM_rasterpos_clip GL_IBM_texture_mirrored_repeat GL_KHR_debug GL_KTX_buffer_region GL_NVX_conditional_render GL_NVX_gpu_memory_info GL_NV_ES1_1_compatibility GL_NV_blend_square GL_NV_conditional_render GL_NV_copy_depth_to_color GL_NV_copy_image GL_NV_depth_buffer_float GL_NV_depth_clamp GL_NV_explicit_multisample GL_NV_fence GL_NV_float_buffer GL_NV_fog_distance GL_NV_fragment_program GL_NV_fragment_program2 GL_NV_fragment_program_option GL_NV_framebuffer_multisample_coverage GL_NV_geometry_shader4 GL_NV_gpu_program4 GL_NV_half_float GL_NV_light_max_exponent GL_NV_multisample_coverage GL_NV_multisample_filter_hint GL_NV_occlusion_query GL_NV_packed_depth_stencil GL_NV_parameter_buffer_object GL_NV_parameter_buffer_object2 GL_NV_path_rendering GL_NV_pixel_data_range GL_NV_point_sprite GL_NV_primitive_restart GL_NV_register_combiners GL_NV_register_combiners2 GL_NV_shader_buffer_load GL_NV_texgen_reflection GL_NV_texture_barrier GL_NV_texture_compression_vtc GL_NV_texture_env_combine4 GL_NV_texture_expand_normal GL_NV_texture_multisample GL_NV_texture_rectangle GL_NV_texture_shader GL_NV_texture_shader2 GL_NV_texture_shader3 GL_NV_transform_feedback GL_NV_transform_feedback2 GL_NV_vdpau_interop GL_NV_vertex_array_range GL_NV_vertex_array_range2 GL_NV_vertex_buffer_unified_memory GL_NV_vertex_program GL_NV_vertex_program1_1 GL_NV_vertex_program2 GL_NV_vertex_program2_option GL_NV_vertex_program3 GL_S3_s3tc GL_SGIS_generate_mipmap GL_SGIS_texture_lod GL_SGIX_depth_texture GL_SGIX_shadow GL_SUN_slice_accum
M
MichaelAtOz
Sun, Aug 30, 2015 11:48 PM

Reassignments should generally be avoided, see this section of the  manual
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/General#Variables  .

The error you got is because the scope of 'c' is established when it is 1st
defined, at which point 'b' does not exist. So when it is finally evaluated
it can't find 'b'.

A variable retains the last assignment, try this;

module test()
{
a = 1;
echo("a:", a, "b:", b, "c:", c);
b = 2;
echo("a:", a, "b:", b, "c:", c);
c = 9;
echo("a:", a, "b:", b, "c:", c);
c = a + b;
echo("a:", a, "b:", b, "c:", c);
}

test();

Unless specifically shown otherwise above, my contribution is in the Public Domain; To the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. This work is published globally via the internet. :) Inclusion of works of previous authors is not included in the above.

The TPP is no simple “trade agreement.”  Fight it! http://www.ourfairdeal.org/

View this message in context: http://forum.openscad.org/Odd-module-variable-assignment-behavior-tp13651p13654.html
Sent from the OpenSCAD mailing list archive at Nabble.com.

Reassignments should generally be avoided, see this section of the manual <https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/General#Variables> . The error you got is because the scope of 'c' is established when it is 1st defined, at which point 'b' does not exist. So when it is finally evaluated it can't find 'b'. A variable retains the last assignment, try this; module test() { a = 1; echo("a:", a, "b:", b, "c:", c); b = 2; echo("a:", a, "b:", b, "c:", c); c = 9; echo("a:", a, "b:", b, "c:", c); c = a + b; echo("a:", a, "b:", b, "c:", c); } test(); ----- Unless specifically shown otherwise above, my contribution is in the Public Domain; To the extent possible under law, I have waived all copyright and related or neighbouring rights to this work. This work is published globally via the internet. :) Inclusion of works of previous authors is not included in the above. The TPP is no simple “trade agreement.” Fight it! http://www.ourfairdeal.org/ -- View this message in context: http://forum.openscad.org/Odd-module-variable-assignment-behavior-tp13651p13654.html Sent from the OpenSCAD mailing list archive at Nabble.com.
N
Neon22
Mon, Aug 31, 2015 12:56 AM

Personally I get around these problems by always making a new variable and
never reusing one.
//
a=1;
b=2;
c=3;

useful_c = (c==3) ? a+b : c;
echo(str("useful_c = ", useful_c));

// Its always easier if you name your variables based on
//  what they do instead of this arbitrary kind of example.
// E.g.

Width = 3;
Height = 2;
Angle = 45;
$fn = 42;

rotate([0,0,Angle]) {
mywidth = cos(Angle) * Width;
depth = mywidth/2;
echo(mywidth, depth, cos(Angle));
//
resize([mywidth,depth,1]) {
sphere(1);
translate([0,0,-Height])
cylinder(r=1, h=Height);
}
}

Ive noticed a strategy that many "Customizer" writers use which is to
Capitalise the variables you intend the user to modify, then use lower case
for internal adjusted versions of those same variables. (Caps show up nicely
in the UI).

However its generally acknowledged that just changing case like this is very
bad for readability and trying to find your bugs. But that's a completely
different flamewar...

--
View this message in context: http://forum.openscad.org/Odd-module-variable-assignment-behavior-tp13651p13655.html
Sent from the OpenSCAD mailing list archive at Nabble.com.

Personally I get around these problems by always making a new variable and never reusing one. // a=1; b=2; c=3; useful_c = (c==3) ? a+b : c; echo(str("useful_c = ", useful_c)); // Its always easier if you name your variables based on // what they do instead of this arbitrary kind of example. // E.g. Width = 3; Height = 2; Angle = 45; $fn = 42; rotate([0,0,Angle]) { mywidth = cos(Angle) * Width; depth = mywidth/2; echo(mywidth, depth, cos(Angle)); // resize([mywidth,depth,1]) { sphere(1); translate([0,0,-Height]) cylinder(r=1, h=Height); } } Ive noticed a strategy that many "Customizer" writers use which is to Capitalise the variables you intend the user to modify, then use lower case for internal adjusted versions of those same variables. (Caps show up nicely in the UI). However its generally acknowledged that just changing case like this is very bad for readability and trying to find your bugs. But that's a completely different flamewar... -- View this message in context: http://forum.openscad.org/Odd-module-variable-assignment-behavior-tp13651p13655.html Sent from the OpenSCAD mailing list archive at Nabble.com.
R
runsun
Mon, Aug 31, 2015 5:41 AM

Cerin wrote

module test()
{
a = 1;
c = 3;
b = 2;
c = a + b;
}

In OpenSCAD, the above code is treated as:

module test()
{
a = 1;

c = a + b;

//<======
b = 2;
c = a + b;
}

Imagine that OpenSCAD scans the code twice, the first time "updates" the
definition to the last one (in this case, changes c=3 to c=a+b), and the 2nd
time executes it. So when it executes, it can't find b, 'cos b hasn't
defined yet.

So, whenever OpenSCAD tells you "Unknown variable XXX", it could be that XXX
is really not yet defined (which is easy to find), or it's some other var
that uses XXX at the time XXX not yet defined (but it won't tell you who
this some "some other var" is).

This is a thing that can be very annoying, especially when the code grows up
to thousands of lines. But it's the nature of OpenSCAD. Just have to deal
with it.

$  Runsun Pan, PhD

$ -- libs: doctest , faces ( git ), offliner ( git );

tips: hash( 1 , 2 ), sweep , var

$ -- Linux Mint 17.1 Rebecca x64  + OpenSCAD 2015.03.15/2015.04.01.nightly

--
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Cerin wrote > module test() > { > a = 1; > c = 3; > b = 2; > c = a + b; > } In OpenSCAD, the above code is treated as: > module test() > { > a = 1; > * > c = a + b; * > //<====== > b = 2; > c = a + b; > } Imagine that OpenSCAD scans the code twice, the first time "updates" the definition to the last one (in this case, changes c=3 to c=a+b), and the 2nd time executes it. So when it executes, it can't find b, 'cos b hasn't defined yet. So, whenever OpenSCAD tells you "Unknown variable XXX", it could be that XXX is really not yet defined (which is easy to find), or it's some other var that uses XXX at the time XXX not yet defined (but it won't tell you who this some "some other var" is). This is a thing that can be very annoying, especially when the code grows up to thousands of lines. But it's the nature of OpenSCAD. Just have to deal with it. ----- $ Runsun Pan, PhD $ -- libs: doctest , faces ( git ), offliner ( git ); tips: hash( 1 , 2 ), sweep , var $ -- Linux Mint 17.1 Rebecca x64 + OpenSCAD 2015.03.15/2015.04.01.nightly -- View this message in context: http://forum.openscad.org/Odd-module-variable-assignment-behavior-tp13651p13658.html Sent from the OpenSCAD mailing list archive at Nabble.com.
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