seq-compiler 6.0.0

Compiler for the Seq programming language
Documentation 
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# Control-flow combinators for Seq
#
# Built on top of `if`, the conditional combinator.
#
# ## Available Words
#
# - when:   ( ..a Bool [ ..a -- ..a ] -- ..a )   Run quotation only when condition is true
# - unless: ( ..a Bool [ ..a -- ..a ] -- ..a )   Run quotation only when condition is false
#
# ## Examples
#
#   x 0 i.> [ "positive" io.write-line ] when
#   x 0 i.= [ "zero!"    io.write-line ] unless
#
# ## Notes
#
# - The quotation must leave the stack shape unchanged (same in/out row).
#   This is what makes `when` and `unless` one-armed: there's no else
#   branch to unify against, so the no-op `[ ]` empty quotation must be
#   compatible with the active branch.

# --------------------------------------------------------------------------
# when — run quotation only when condition is true
# --------------------------------------------------------------------------
# Push an empty quotation as the else-branch and dispatch through `if`.
: when ( ..a Bool [ ..a -- ..a ] -- ..a )
  [ ] if
;

# --------------------------------------------------------------------------
# unless — run quotation only when condition is false
# --------------------------------------------------------------------------
# Stack at entry: ( ..a Bool quot ). We push `[ ]` (empty quotation),
# then `swap` so the layout becomes ( ..a Bool [ ] quot ) — i.e. the
# user's quotation is now the else-branch. `if` then runs the user's
# quotation when the Bool is false, and the empty quotation (no-op)
# when true.
: unless ( ..a Bool [ ..a -- ..a ] -- ..a )
  [ ] swap if
;