Reverse Polish Notation

Ajisai uses RPN (postfix notation). Operators follow operands:

# Traditional: (1 + 2) * 3
# Ajisai:
[ 1 ] [ 2 ] + [ 3 ] *    # Result: [ 9 ]

Basic Elements

Comments

# This is a comment
[ 1 2 3 ]  # Inline comment

Numbers

42        # Integer
3.14      # Decimal (stored as fraction)
1/3       # Fraction
-5        # Negative
1.5e2     # Scientific notation

Strings

'hello'
'日本語'    # UTF-8 supported

Booleans & Nil

TRUE
FALSE
nil

Vectors

# 1D Vector
[ 1 2 3 ]

# 2D Nested Vector
[ [ 1 2 ] [ 3 4 ] ]

# Mixed types
[ 1 'hello' TRUE [ 2 3 ] ]

# All brackets equivalent
[ 1 2 3 ]
{ 1 2 3 }
( 1 2 3 )

Defining Words

Use code block syntax { ... } (or ( ... )) to define words:

# Define a word
{ [ 2 ] * } 'DOUBLE' DEF

# Use it
[ 5 ] DOUBLE    # Result: [ 10 ]

# Check if even
{ [ 2 ] MOD [ 0 ] = } 'EVEN?' DEF
[ 4 ] EVEN?     # Result: [ TRUE ]

Operation Targets

Stack Top Mode (default)

[ 1 2 3 ] LENGTH    # Operates on top element

Stack Mode (..)

a b c .. LENGTH     # Operates on entire stack
a b c .. REVERSE    # Result: c b a

Pipeline Operator (==)

Visual marker for data flow (no-op). Makes complex transformations readable:

[ 1 2 3 4 5 ]
  == { [ 2 ] * } MAP           # Double each
  == { [ 5 ] < NOT } FILTER    # Keep >= 5
  == [ 0 ] { + } FOLD          # Sum

Nil Coalescing Operator (=>)

Returns alternative value when first value is NIL:

NIL => [ 0 ]       # Result: [ 0 ] (NIL replaced)
[ 42 ] => [ 0 ]    # Result: [ 42 ] (non-NIL preserved)

# Useful for default values
'key' LOOKUP => [ 'default' ]

Input Helpers