========================
SHORT TERM =============  (for curvature-based VR)
========================

IL support for higher-order tensor values (matrices, etc).
    tensor construction
    tensor indexing and slicing
    verify that hessians work correctly

Outer products
    syntax [DONE]
    typechecking
    IL and codegen

Add M dot v, v dot M, and M dot N

Identity matrix [DONE up to code generation]

trace [DONE]

extend norm (|exp|) to tensor[3,3]

Use ∇⊗ etc. syntax
    syntax [DONE]
    typechecking
    IL and codegen

Add sequence types
    syntax
	types: ty '{' INT '}'
	value construction: '{' e1 ',' … ',' en '}'
	indexing: e '{' e '}'

Infix dot product and cross product [DONE]

lerp on scalars and vectors [DONE]

==============================
other SHORT TERM =============  (including needed for LIC)
==============================

determinant ("det") for tensor[3,3]

Decide if we want to allow redefinitions of variables
  (as in vr-lite-cam.diderot)

extend norm (|exp|) to all tensor types

extend normalize to all tensor types

vector fields: convolution on vector images

expand trace in mid to low translation

value-numbering optimization

Add type aliases for color types
    rgb = real{3}
    rgba = real{4}

==============================
MEDIUM TERM ================== (needed for streamlines & tractography)
==============================

ability to emit/track/record variables into dynamically re-sized
runtime buffer

evals & evecs for symmetric tensor[3,3]

tensor fields: convolution on general tensor images

==============================
other MEDIUM TERM ============ (needed for particles)
==============================

run-time birth and death of strands

"initially" supports lists

"initially" supports lists of positions output from 
different initalization Diderot program

spatial data structure that permits strands' queries of neighbors

proper handling of stabilize method

==============================
LONG TERM ==================== 
==============================

co- vs contra- index distinction

add ":" for tensor dot product (contracts out two indices
instead of one like •), valid for all pairs of tensors with
at least two indices

some indication of tensor symmetry
(have to identify the group of index permutations that are symmetries)

dot works on all tensors

outer works on all tensors

Einstein summation notation

"tensor comprehension" (like list comprehension)

======================
BUGS =================
======================

test/mip-cam.diderot:
    // generated C code looks like "(float)p_ui_0--0.5e0f"
    //real rayU = 2.0*camUmax*(real(ui) - -0.5)/real(imgResU) - camUmax;

test/vr-kcomp.diderot:
    // HEY (scoping BUG): the strand parameters (e.g. ui, vi) ...

test/zslice2.diderot:
// but is this not valid syntax for creating field in one shot?
//field#2(3)[] F = (load("../data/zimg112.nrrd")) ⊛ bspln3;
// It is valid syntax, but there is a bug in the conversion from HighIL to MidIL

test/zslice2.diderot:
// HEY (bug) bspln5 leads to problems ...
//  uncaught exception Size [size]
//    raised at c-target/c-target.sml:47.15-47.19
//field#4(3)[] F = img ⊛ bspln5;