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-rw-r--r--julia/minimal.jl128
-rw-r--r--julia/sexpr.jl119
2 files changed, 247 insertions, 0 deletions
diff --git a/julia/minimal.jl b/julia/minimal.jl
new file mode 100644
index 0000000..303b87a
--- /dev/null
+++ b/julia/minimal.jl
@@ -0,0 +1,128 @@
+
+# A partial Scheme implementation in Julia
+
+# null -> nothing
+# pair -> Pair type
+# boolean (true/false) -> true/false
+# number -> Number
+# identifier/symbol -> symbol
+
+is_atom(x) = x == () || !(x == nothing ||
+ typeof(x) <: Tuple ||
+ typeof(x) <: Array ||
+ typeof(x) <: Dict)
+is_null(x) = x == ()
+is_zero(x) = x == 0
+is_eq(a, b) = a == b
+is_number(x) = typeof(x) <: Number
+is_boolean(x) = x == true || x == false
+is_builtin(x) = x in (:lambda, :quote, :cond, :else, :cons, :car, :cdr,
+ :isnull, :iseq, :isatom, :iszero, :isnumber,
+ :+, :-, :*, :/, +, -, *, /)
+
+identity_action(x, ctx) = x
+lookup_action(x, ctx) = ctx[x]
+quote_action(x, ctx) = length(x) == 2 ? x[2] : throw(ErrorException())
+
+function cond_action(x, ctx)
+ for line in x[2:end]
+ if line[1] == :else
+ return meaning(line[2], ctx)
+ elseif meaning(line[1], ctx)
+ return meaning(line[2], ctx)
+ else
+ # "unspecified"
+ return nothing
+ end
+ end
+end
+
+function lambda_action(x, ctx)
+ return (:procedure, x[2], x[3:end], copy(ctx))
+end
+
+function apply_action(x, ctx)
+ if is_builtin(x[1])
+ action = x[1]
+ args = [meaning(y, ctx) for y in x[2:end]]
+ if action == :cons
+ return tuple(args[1], args[2])
+ elseif action == :car
+ return args[1][1]
+ elseif action == :cdr
+ return args[1][2]
+ elseif action == :isnull
+ return is_null(args[1])
+ elseif action == :iseq
+ return is_eq(args[1], args[2])
+ elseif action == :isatom
+ return is_atom(args[1])
+ elseif action == :iszero
+ return is_zero(args[1])
+ elseif action == :isnumber
+ return is_number(args[1])
+ elseif action == :+ || action == +
+ return args[1] + args[2]
+ elseif action == :- || action == -
+ return args[1] - args[2]
+ elseif action == :* || action == *
+ return args[1] * args[2]
+ elseif action == :/ || action == /
+ return args[1] / args[2]
+ else
+ throw(ErrorException("Unexpected builtin: $(x[0])"))
+ end
+ elseif typeof(x[1]) <: Tuple
+ proc = meaning(x[1], ctx)
+ if proc[1] != :procedure
+ throw(ErrorException("Not applicable: $(str(proc))"))
+ end
+ variables = proc[2]
+ body = proc[3]
+ closure = copy(proc[4])
+ args = [meaning(y, ctx) for y in x[2:end]]
+ for i in 1:length(variables)
+ closure[variables[i]] = args[i]
+ end
+ ret = nothing
+ for expr in body
+ ret = meaning(expr, closure)
+ end
+ return ret
+ else
+ throw(ErrorException("Unexpected... thing...: $(x[1])"))
+ end
+end
+
+function meaning(x, ctx)
+ action = nothing
+ if is_atom(x)
+ if is_number(x) || is_boolean(x) || is_builtin(x)
+ return identity_action(x, ctx)
+ elseif typeof(x) <: Symbol
+ return lookup_action(x, ctx)
+ end
+ elseif typeof(x) <: Tuple
+ if x[1] == :quote
+ return quote_action(x, ctx)
+ elseif x[1] == :cond
+ return cond_action(x, ctx)
+ elseif x[1] == :lambda
+ return lambda_action(x, ctx)
+ elseif typeof(x[1]) <: Tuple
+ return apply_action(x, ctx)
+ else # some other identifier, either builtin or not
+ return apply_action(x, ctx)
+ end
+ end
+ throw(ErrorException("Unexpected expression: $x"))
+end
+
+function value(ast)
+ return meaning(ast, Dict())
+end
+
+function test_minimal_scheme()
+ @assert 6 == value( ((:lambda, (:x, ), (+, 1, :x)), 5) )
+ value( (:car, (:quote, (1, 2, 3, 4))) )
+end
diff --git a/julia/sexpr.jl b/julia/sexpr.jl
new file mode 100644
index 0000000..1a0ba3c
--- /dev/null
+++ b/julia/sexpr.jl
@@ -0,0 +1,119 @@
+
+"""
+Takes a string 's' and will convert it to an Int64 or Float64 (if possible), or
+return the string if not.
+"""
+function trynum(s::AbstractString)
+ # Test for: only number chars, and optionally a single decimal (period),
+ # but not just a single decimal on it's own ("." is not a number).
+ # Also allow a '-' in the first position.
+ # Could have just try/caught around Julia's float(), used below.
+ decimal_count = 0
+ dash_count = 0
+ for (i, c) in enumerate(s)
+ if c == '.'
+ decimal_count += 1
+ elseif c == '-' && i == 1 && length(s) > 1
+ dash_count += 1
+ elseif !(c in "1234567890")
+ return s
+ end
+ end
+ if decimal_count > 1 || decimal_count + dash_count >= length(s)
+ return s
+ end
+ # Haven't written our own string-to-number function; use Julia's
+ if decimal_count > 0
+ return float(s)
+ else
+ # Julia 0.4.3 complains with "use parse(Int,s) instead" of int(s)
+ return parse(Int, s)
+ end
+end
+
+"""
+Take a string 's' and splits it into elements (based on 'ws' white space
+characters) and tuples (based on 'sep' separators).
+"""
+function tokenize(s::AbstractString; sep="()", ws=" \t\n")
+ L = AbstractString[]
+ food = 0 # num of yummy non-whitespace characters we have just eaten
+ for (i, c) in enumerate(s)
+ if c in sep || c in ws
+ if food > 0
+ push!(L, s[i-food:i-1])
+ end
+ if c in sep
+ push!(L, string(c))
+ end
+ food = 0
+ elseif i == length(s)
+ push!(L, s[i-food:end])
+ # will break next iteration
+ else
+ food += 1
+ end
+ end
+ # Convert Array of strings to an (immutable) Tuple
+ return tuple(L...)
+end
+
+"""
+Helper for `parse()`.
+
+Returns two values: the parsed expression, and the number of tokens consumed.
+
+Note that this function always returns a Tuple, even if only a single token is
+passed: calling code must unwrap. Also, this will only parse out the first
+complete expression, silently discarding trailing elements.
+
+Should probably use value exceptions instead of @assert on failure
+"""
+function _parse_tokens(tokens, depth=0)
+ L = []
+ i = 1
+ while i <= length(tokens)
+ el = tokens[i]
+ if el == "("
+ (expr, skip) = _parse_tokens(tokens[(i+1):end], depth + 1)
+ push!(L, expr)
+ i += skip
+ elseif el == ")"
+ @assert depth > 0 "Missing open bracket..."
+ return (tuple(L...), i+1)
+ else
+ push!(L, el)
+ i += 1
+ end
+ end
+ @assert depth == 0 "Missing close bracket..."
+ return (tuple(L...), i)
+end
+
+"""
+Takes a string and returns a tuple-based pseudo AST.
+
+Notes: all numbers are converted to Float64. No weird special characters are
+parsed specially (eg, comma, pipe, hash, etc).
+"""
+function parse(s::AbstractString)
+ # First split into a flat list...
+ tokens = tokenize(s)
+
+ # ... then convert any numbers ...
+ tokens = map(trynum, tokens)
+
+ # ... then parse into nested tuples.
+ (expr, sz) = _parse_tokens(tokens)
+
+ # Unwrap the first element and return that.
+ return expr[1]
+end
+
+# parse("1")
+# parse("((()) ())")
+# parse("(a 134 ( 4 5 6) 2 ( ))")
+# parse("(asdf 134 ( 4 5 6) 2 ( ))")
+# parse("(1 2 3 -4567 123.25624 . -.)")
+# parse("(1 2 3 -4567 123.25624 .1 1. -.1 -1. - . -.)")
+# parse("(first (list 1 (+ 2 3) 9))")